Sounds like you are using the Footage Panel instead of the Comp Panel. I strongly suggest that you start by opening the Learn workspace and going through the tutorials. Then spend some time with the User Guide.
After Effects is not a video editing app, it is designed to create shots, not edit a video to the beat of the music. Most comps are one shot, a composite, or a motion graphic, and the average length of most of my comps is under seven seconds because most shots in most movies are less than seven seconds.