Describing how a muscle contracts was one of the banes of my medical school career, but I need not have struggled so hard. There are numerous really good animations on the topic. Once you can see the mechanism, it's much easier to describe it. I've come across two good animations of the process:
The first one is from a website of the textbook "NEUROBIOLOGY, Molecules, Cells and Systems (2nd edn.)", by Gary G. Matthews. There is a basic text and a nice set of animations. You need Flash Player to view it, though.
The only part that I didn't think was that well explained was myosin's 'power strokes'. That is more than remedied by this outstanding video (on YouTube) that comes with commentary too. I'd recommend watching both - they complement each other nicely.
Now it'll be easier to learn!
P.S. If anyone else knowns of other good animations, be sure to let me know...