I don't understand the question you are asking.
If you are saying that you want to cut or edit a video in After Effects, you should not do that. You should use Premiere or some other video editing program. After Effects is for creating effects shots, compositing, and motion graphics. It is not intended for editing.
If you are asking how to get playback of your timeline so you can see what sort of effects you are creating, go through all of the resources that Mylenium linked in his post. After Effects is not like a video editing program and it will take some time to understand the basic, foundational aspects of it.