You need to be much more specific about exactly what you're doing and what exactly the result is. Error messages? If so, then what is the exact message? Screenshots help.
In general, please provide answers to the questions listed here: "FAQ: What information should I provide when asking a question on this forum?"
First, I want to clear up some vocabulary issues. After Effects is not intended for editing video. Editing involves cutting shots together to tell a story. Premiere Pro edits video. While you technically can cut video together in AE, Premiere is much, much better for that.
After Effects is used for creating shots - visual effects, compositing, motion graphics, animation, color correction, color grading, etc.
What exact version number of AE (down to the decimal points) are you using? Plus the questions Todd asked, plus the info in the link he gave.
Also, if you're new to AE, you should really start here. This resource will give you a foundation in how to actually use After Effects that will probably clear up your current problem and prevent much more frustration in the future.