How to reformat and re-install an old G5

I was given an old G5, and the existing installed OS is locked, and I don't have the password. I don't care about erasing its whole content. I have a bunch of CDs, and I want to know how can I restart this machine so it boots from the CD and reformat the whole system. I am very new to MAC world. I realise this is a MAC 101 question type, but I need to start somewhere...... Thanks :-)