How to film what is happening on your computer screen?
I've seen YouTube videos where they film strictly what's on the screen.
Fraps works great, but can slow down some depending one what you are doing, but overall still works amazing compared to other softwares. Besides, it's free.
You download a screen capture software.
Even to the highest professional level (Gamers XP) Fraps is about 30 bucks and is very good, just make sure you have low settings on whatever your doing because Fraps will lower your fps pretty bad if your not running a good pc