There are all kinds of screen recorders out there. I have friends who use Jing, SMART Recorder, Snag-it, and others but they all have limits in terms of use and/or cost. I'll throw one more in the mix that might just be a cut above.

With a free Screencast-o-matic account you can record videos up to 15 minutes in length ($9 per year for a 60 minute-per-video limit). That means you can record a part of your lesson to post on your class webpage, sub plans, or a tutorial for students or colleagues to walk them through a process - like this one by New Prague's Shawn Brandt showing how to use Screencast-o-matic. Best of all, it works right in your browser with no download or install required!

Give it a try, and share the link as a comment here, so others can learn from your great work!