ACTV offers producers the use of iMovie...so here is a great place to start as a beginner. Eric Timmer produced and posted great information on his YouTube Channel. His tutorial covers iMovie 10.0.5 but will work when learning older versions as well.
Remember that when you come to ACTV to work on a project the staff will be available to assist you as well. However, you can learn a great amount of information at your leisure with these and other tutorials.
iMovie for Beginners: Runtime 30:05
Here is a link that contains an entire playlist of iMovie Tutorials:
More Tutorials Here