codec's are used to save .avi files and compress them to take up less space.
You should not worry too much about this because you should not use a codec that is not included in Windows anyway (otherwise your end users have to identify, locate, download and install the codec you've used).
When you make your animation you will get a choice of codec much like art programs let you save .jpg or .bmp. Just pick a few off the list and see which one works best for your animation.

God created the world in 7 days, but we're still waiting for the patch.