We have a God given right to keep and bear arms and if you live in a country that recognizes that fundamental right then you should exercise that right by getting guns, and if you don't you should either consider relocating or more realistically realize that you aren't the target audience of this article. Now of course not all guns are equal and not all of them serve the same purpose so you should have more than one, in fact (as you can tell from the title) I believe that there are six that I believe everyone should own in order to cover every use case and I've listed them roughly in the order that I believe you should acquire them (although this is not the order I got mine in), so I'll save any other ramblings I may have for the end of all of this although I will assume that you are familiar with gun vocabulary but I may provide a few mistaken definitions at the bottom of this page.
A decent .22 caliber rifle is cheap to buy, cheap to shoot, fun to use, have almost no recoil, and they are the perfect first gun for anyone because they are easy to learn to shoot with. Your first .22 should also be simple, it should have open sights so that you don't train yourself to be reliant on a scope or a red-dot optic and it should be semiautomatic so that when you are trying to master the art of a controlled trigger pull without having to fumble around with any other controls between shots, and then once you have mastered that art you can have fun shooting things fast.
Many gun enthusiasts today dismiss the .22 and forget their importance and utility. My dad once went into a gun store and described the benefits of a .22 to the salesman there to see if he would point him to a .22 rifle but the salesman failed to do that because he'd forgotten the glory of a .22. Is this the most boring gun on my list? Yes, but I do believe it is the most important and despite there being cooler guns out there it is still fun, a couple weeks ago I was using it to shoot a 6 inch plate at 50 yards and it was great fun to hit something that appeared smaller than my front sight.
Now after you've mastered the slow controlled trigger pull necessary to accurately shoot a rifle you'll want to forget that because shotguns are completely different animals. Shotguns are designed for shooting small fast-moving targets at close range with the most common practical use being bird hunting. Of course you could use a shotgun to shoot at stationary targets but unless you are just doing it to see a watermelon explode shooting them at stationary targets is pretty lame because it requires no actual skill. You could also load a shotgun up with a slug and shoot something 100 yards with questionable accuracy but why would you do that when you could use a gun that's actually designed to do that?
Anyways I'm starting to get off topic there, so why own a shotgun? Because they're fun. Skeet shooting is fun. Get a shotgun with a bead sight and find a friend with a clay pigeon thrower, find a good teacher, and get shooting. I'd recommend a pump action shotgun just because they're cool and I don't see much of a benefit to a semiautomatic shotgun and I recommend 12 gauge because it is the most common (and because I think 20 guages are dumb) but at the end of the day a shotgun is a shotgun so just get a reliable one like a Mossberg 500, or a Remington 870.
The right to keep and bear arms includes actually bearing arms, and in other words carrying a gun and these days you don't want it to be obvious to people that you have a gun on you so if you do carry you should carry concealed. In the last decade or so several great concealed carry oriented guns have come out, the Smith & Wesson M&P Shield, the Sig P365, and the Springfield Armory Hellcat are just a few of the notable ones, and you should have a handgun that you feel comfortable carrying.
That being said I don't think everyone should carry, drawing a gun on someone should be the last thing you'd ever want to do and if you don't understand that then you have no business carrying a gun. However I do believe that everyone should take a concealed carry class at some point in their life because those classes teach the laws and ethics behind carrying a gun which everyone should be aware of and consider. Such a class also teaches gun safety which is something that everyone should be familiar with regardless of whether or not they own a gun.
This is probably the easiest gun to explain on the list, you want a rifle that is designed for long range shots and surprisingly you don't have to pay too much money these days for a gun that can shoot 1,000 yards. Now are you or I ever going to shoot at targets that far away? Probably not, that takes a lot of practice, skill, and access to a range not many people are blessed with but a gun that can shoot 1,000 yards can easily shoot one or two hundred yards which is a much more reasonable distance for the average person and still quite rewarding, plus you can take it hunting.
What I mean by a full-sized handgun is something like a Glock 19, a handgun the size that most cops carry and that typically have standard magazines with a capacity of 15 rounds or more. Many gun enthusiasts will that guns like these are great because you can slap a flashlight on them, an optic, and even a suppressor (if you're willing to jump through those hoops) and they can be a great home defense gun, or truck gun, or all-around gun, or whatever, heck some people are even crazy enough to concealed carry massive guns like that, and while I'm not going to argue that those can be good reasons but they're not all that appealing to people outside the gun world and are very different from my simple reason to own one.
I believe that if you own guns you should get good at shooting them and the best type of handgun to get good with is a full-sized one chambered in 9mm or something similar. Because these guns are big their recoil is easier to control than the recoil of a smaller gun. You could of course get a handgun chambered in .22 that would recoil much less but recoil control is a very important part of pistol shooting so by practicing with a low recoil handgun you'd probably be doing yourself a disservice in the long run (plus .22 caliber handguns are usually unreliable). By practicing with a full-sized handgun you are setting yourself up for success.
Now I did mention the Glock 19 here but that was only to get you to understand what I was talking about. While Glocks have become the gun that every other handgun is compared to these days and are the most popular handgun I wouldn't recommend buying one. Glocks have bad ergonomics, terrible sights, an average trigger, and a slide that isn't the easiest to grip; it is not uncommon for a gun enthusiast to spend $600 on a new Glock then spend at least another three to four hundred dollars modifying their Glock to get rid of all of those shortcomings, the better thing to do would be to buy a Walther or an M&P, there are plenty of great alternatives. But the biggest reason why I wouldn't recommend a Glock to a new shooter is the fact that they lack a manual safety, this really isn't that big of a deal to people comfortable with guns but using a manual safety is something that can help keep you safe, Glocks may be the highest sold handgun but they are also the highest returned handgun because of their lack of a manual safety so that is something that you may want to consider.
There is a lot of stigma around the AR-15 that has been caused by people seeking to take your rights away and you shouldn't pay attention to it. Really the only differences between an AR-15 and the cheap .22 I recommended first are the caliber (obviously), the fact that AR-15s are easy to mount things to, and the fact that AR-15s take easily found 30 round magazines. Sure AR-15s look different but they are functionally the same as any other semiautomatic rifle, the AR-15 isn't even the most powerful gun on this list, it's number three.
The AR-15 is the modern American musket, I stated in an article a few months ago they are a symbol of independence, if things started to go south and you found yourself in danger of conflict and responsible for your own protection this is the gun you'd want to have with you. But more importantly, they're fun. Powerful rifles are fun to shoot things with and the 5.56 and .223** rounds that are typically shot by AR-15s are inexpensive and with a simple 1x6 optic you can have a lot of fun at both close and relatively far distances. Just make sure that you get a good AR from a reputable company, you don't want to pay less than $800.
The AR-15 is not an assault weapon but it is (as DistroTube puts it) a freedom rifle. There is no real definition of an assault weapon or assault rifle, these terms really just mean any gun that corrupt government bureaucrats don't want you to own which could change at any moment and it is important to remember that the true purpose of the second amendment is not for self defense, hunting, or sport shooting, it is for protection against corrupt government bureaucrats. However I do hope that there is never a point in which violence needs to occur in order to protect our freedoms.
Are these the only six kinds of guns you should own? No. Lever actions are cool, revolvers are cool, AKs are cool, AR pistols chambered in 300 blackout with integrated suppressors are cool, muzzle loaders are cool, 1911s are cool, historic guns are cool, all guns are cool and I'm not saying these are the only six guns you should buy. These six guns are what you need and have practice with in order to be a well rounded gun owner. Get training, be safe, and don't do anything stupid.
* - semiautomatic: a term used to describe any gun which fires one bullet per trigger pull and automatically chambers the next round so that the user of that gun does not need to perform any action other than pulling the trigger to operate that gun assuming the gun is loaded and operating properly
** - The 5.56 and .223 have identical dimensions and it is not uncommon to find ARs chambered in either one of these but you should get one chambered in 5.56 because that round generates a bit more pressure so guns built for that are more versatile, a gun chambered in 5.56 can safely shoot both a 5.56 and .223 cartridge although it is best just to stick with one as the ballistics of the two rounds differ slightly.