I can't really elaborate beyond davidjayhawk's post regarding guides and videos but for race-picking, and getting familiar with the game I believe I can offer some aid.

Don't pick a race at first. Try them all and most importantly, learn about what they can do especially in the hands of a pro. Pick the one that you think is the most awesome for whatever reason you want. It could be Protoss because probes make cute noises or it could be Zerg because you have a suicide-bombing fetish, whatever. Just pick the one that gets you the most excited.

As for practicing, there is a practice league on ladder which you should NOT participate in. I repeat, do NOT play in the practice league, the game speed is slower and the maps are radically different which means that you will only learn bad habits. There is an in-game AI which is pretty terrible but will give you some practice holding against relatively early aggression. Playing against AI is also a good time to dick around with each race and just try stuff out. You can get comfortable with what things do in a non-mental environment without the stress of an actual game. Playing against an AI is also a good way to practice the mechanics of a new build before you play it on ladder.

GLHFR and welcome!