Here’s a great article from Musictech dot Net that explains the basics of microphone type, polar patterns, frequency responses, and lots of other stuff that an audio engineer needs to know about microphones.
It may seem like a trivial subject to the un-initiated, but along with mic positioning and preamp selection, it’s some of the most important stuff you’ll need to know. But don’t worry if you can’t learn it all in one go, that’s where you just need to experiment as you go. Whenever you have a chance, just plug in every mic you can lay your hands on, and see what sounds you can get out of them. Articles like these can point you in the right direction, but the only way to get really good is trial & error.
So in the end, probably the most important thing to learn is how to take every chance you can to experiment.