Camstudio is a program/application for the Windows operating system that records what is on the screen. So if you wanted to record yourself playing a round of Call of Duty on the computer, you could use Camstudio to record the match. So if you start a recording, then draw a picture on paint, you can see what you did step by step. The nice thing about Camstudio as opposed to other programs is it's opensource. This is nice because it means it's free. Not only that, but if you know something about programming, you can download the source code and edit the program yourself for your own needs.