Learn to go to apple.com/support or search google. I made you a shortcut tho... This is taken from the straight from the Mac Installation and Setup guide written by Apple and retrieved from apple.com/support>click on Mac OS on the left side of the page>click on the OS you need help with. All copyrights reside with Apple blah blah blah.
1 Insert the Mac OS X installation disc, and then double-click the Install Mac OS X icon.
2 In the Installer, click Utilities, and then click Restart. 3 When the Language Chooser appears, select your language, and then click the
Continue button (looks like an arrow).
4 Choose Utilities > Disk Utility.
5 Select your disk from the list on the left, and then click the Erase tab.
6 Select Mac OS Extended (Journaled) from the Format pop-up menu, type a name for your disk, and then click Erase.
After the disk has been erased, choose Disk Utility > Quit Disk Utility, and then follow the instructions in the Mac OS X Installer to reinstall Mac OS X.
Seriously tho, search apple.com/support- there's a wealth of knowledge there, and also google it.