The first place to go would probably be the online help and community pages. You'll find a link under Help. There's lots of good stuff there.
The second place is to try a search on Google. You could spend the next 6 months just working through the free tutorials that are out there.
If you want to spend a month or so on a well organized crash course you can try Lynda.com. Their monthly subscription is very affordable. Then there are a bunch of other folks that have online and disk based training. You can also try your community colleges. Many have AE and Photoshop classes for next to nothing.
In addition to Rick's suggestions, I recommend using the materials linked to from the "Keying overview and tips" page.
Also, you can get more focused results by using the After Effects Community Help search than by using regular Google search. The After Effects Community Help search engine is a Google custom search engine that just searches websites that are known to have good, free information about Adobe software.
I don't know what you AE experience level is - but Trish and Chris Meyer (two of the top names in AE) have recently created online tutorials through lynda.com. You might want to check it out.
Also, look at their blogs on pro video coalition. <http://provideocoalition.com/index.php/cmg_blogs> and <http://provideocoalition.com/index.php/cmg_keyframes>