Make sure the composition you are working on is selcted, then hit ctrl+k for composition settings (the settings can also be reached via the long way under the "compostion" tab at the top). Then you should see the "duration" box in which you can set the length of your timeline. The notation is: <hours>;<minutes>;<seconds>;<frames>. I usually put more than the length of the project I'm working on to give me some wiggle room.
Hope this helps!
It sounds to me like jess just needs to know how to zoom in the Timeline panel:
Start here to learn After Effects: http://adobe.ly/AE_basics