If by "insert" you mean add a clip onto the timeline....drag and drop it onto the timeline, and that's it.
However I'm willing to bet you mean inserting a clip between two others on the timeline. I asked a very similar question, and the answer is in this stream:
Roger, I know you got your help already and figured it out. But since you mentioned you couldn't find it in what you read, I suggest you give the Show Me How tutorials a try.
Help > Show Me How > How to Add Media to the Timeline. Many other good ones there as well.
Thank You MSmart, I have used the "help" tutorials but feel they do not give the kind of detail one might like. I need to be less lazy in looking there. :)