clean format and reinstall osx

Hi,
This might seem like a noob question, but how do I reinstall OSX after a clean format on mac. I never done it before, also do I need both install dics I seem to have lost disc 1

You might not need both discs, but you'll definitely need disc 1.
To boot from a CD, restart and hold down the C key.

You will need both discs, why the format?

thanks guys I formatted and installed succesfully, i just wanted to format for my brother since I'm giving it to him and he wanted everything cleared off.