Well, let's say you would like to purchase a firearm in the United States, legally.
How do you do that?
Well, you first need to decide what you are buying, which will lead you to discover that different firearms are designed for different uses.
Do you want something to hunt with?
Something to defend yourself (and your family and property) with?
Something to target shoot with?
Let's say you choose hunting, now, do you want something to shoot ducks? Deer? Rabbits? Big Horn Sheep? All these choices define different types of weapons.
And of course, if you wish to do all these things, you would ultimately have different firearms to do each with.
For example, let's say you hunt Deer. You may want a firearm like a .243 or a 30-06. It may be a semi-automatic, lever action, or bolt action rifle, pump action, rolling block, or single shot. It may be a classic design from the early part of the 20th century, or something more modern. It may be you prefer a 30-30. There are many calibers, designed by many manufacturers, in many different style rifles, and all are desinged for hunting certain things, with a certain geography in mind.
I have a cousin who used to shoot coyotes for farmers, he used a very high velocity bullet, with a very high-powered telescopic sight, to shoot them from very long distances. That bullet could have been used to shoot deer, but it wouldn't work as well as ones designed for deer and animals the size of a deer.
Anyway, let's say you choose a common, inexpensive bullet, the .223, for hunting deer. You choose it because it is common, inexpensive and easily available.
Now you need to decide on the rifle you will use... hmm, something classic? Maybe a bolt action rifle? Good choice, unless you think you may not be as good a shot as you would like to be, because that second shot? That takes longer than in a semi-automatic. Maybe you might want to decide on a more modern firearm. Also you have to think about maintaining your firearm, how easy is it to disassemble and clean, and reassemble? How heavy is it? Is it prone to rusting?
So, with these thoughts in mind, you go to the local gun store to buy that rifle.
Ooops, what are the laws in your state? Do you have the appropriate training and licenses to buy the rifle?
Maybe your state has a law requiring a waiting period between when you buy the rifle and when you can actually pick it up? If so, better plan for that too.
Some states have laws that say you need a license to buy bullets. Do you have that as well?
Oh, and don't forget, you will need several forms of id too, and will need to wait for the background check.
Yep, it isn't quite as easy to do this as the Media and anti-gun people would have you believe.
You must obey all these laws scrupulously or you will lose your right to own a firearm, FOREVER , unless you are one of the rich and famous... like a Kennedy. (google John Kennedy firearm, logan airport)