People tend to drink whatever mixed with vodka, Jaegermeister, beer, WKDs (if you can't handle much alcohol!). As for how many it takes to get drunk, it's impossible to say because each individual is vastly different. Obviously, the more you drink the more you become tolerant of it so chances are, for someone who has never tried alcohol before, you won't be able to handle as much as some of your friends. One of my friends can handle 8 or 9 beers without getting even tipsy yet another starts to go silly after 1 and a half (of the same beer), so really there is a vast difference and it would be dangerous for you to drink to an "average" because you simply don't know what you can handle personally.
I'd suggest that, if you're desperate to start drinking, you do it at home first so you can figure out how much you can handle before you go and make an arse of yourself in a pub around people who will probably be too drunk themselves to worry about you. Either that, or go out with a small bunch of friends you trust to not push you past your limits and you know will take care of you just in case you do.
As for what you should drink, the examples I gave above are just examples. Don't drink what others do just because it's cool and you fancy getting drunk. Try different things and see what you enjoy. And if you don't like it, don't drink it just because everyone else does.
Getting drunk is not cool.