[Janelle Roxas]"I am new to AE. I want to learn how to put text and mp3 together."
Welcome to After Effects! It's a complicated bit of software, which means you can't really learn a couple of tricks to get you by. You have to know the basics. Here's a basic: did you know that AE hates compressed audio like mp3 files, and that you have to convert them to something like a wav file?
The good news: once you get past the basics, AE gets fun!
Based on your description above, we really have no clue what you want to do. I could do what you describe in an editing application just as easily. If we tried to describe what to you using AE terminology, you wouldn't know what we meant.
But never fear: Adobe's own Todd Kopriva -- a fine, patient and knowledgeable gent -- has thoughtfully compiled a bunch of information for the AE beginner, and here it is: