Then start with dependable, simple, accurate, and affordable 9mm. Sufficient for self defense, accurate for range work, inexpensive to feed, and simple to clean and maintain.
As you've gathered, there are Glock fans, Walther fans, XD fans (like me), M&P fans, 1911 fans, and many other brands and types to fit your needs.
Start on the brand forums, and learn, learn, learn. Go to the manufacturer's websites, and learn more. Go to a rental range and shoot lots of guns. Revolvers, DAOs, SA/DAs, SAOs... Ahah... What's a SA/DA??? Learn before you buy.
Most guys at 21 have no lack of learning ability, but a significant lack of disposable income... Do your research, spend some money on rentals first to "test-drive" guns. And don't be steered by commission sales guys at the store.
ASK people here, ASK people at the range. We're full of experience. I've learned a TON here and online in the last year. Now I'm building a small collection of guns. One for every nitch...
But the first one? My suggestion is a polymer-framed, 9mm, with as few moving parts as possible... Then when you're ready for more, if ever, move up. Many guys start simple, spend a ton of money on complex fancy guns, then end up carrying a "simple" gun again in the long run.
If it will be for concealed carry, consider:
2) length of grip (shorter is better)
3) length of barrel (shorter is more concealable, longer is more shootable)
Most of all, welcome, enjoy, don't get addicted.
Too late for me.