I’ve been asked a couple of times what application I use to create screen capture movies, I actually use Screenflow and I’d certainly recommend it to anyone who is planning create regular screen recordings. However if it is a one off movie than you can use QuickTime Player, go to the File menu and select “New Screen Recording”.

A small widget appears that offers a couple of options and is used to start the recording.

Once finished stop the recording and you can use Quicktime to do any minor edits or you can use iMovie to do more substantial editing.