You can type "high school football association" in google. It will produce TONS of association websites that have their training material openly available. Many of these associations have Mechanics diagrams in PowerPoint already.
I have searched all of these sites and downloaded all their training materials. If you would like to private message me i would be happy to send you everything i have on mechanics. It might help you start out and give you some ideas.
Rickky is correct Power point is probably the easiest to start with. If you are looking for something WAY more professional i would recommend looking at Adobe products. Adobe InDesign is a great print and digital publishing tool. It is a bit expensive unless you know how to get it for free.

Bjfb... send me a private message i would be interested in helping you get something started. I am also working on revising my associations mechanics training this off season. I would not mind having another person to share ideas with.