Sometimes it makes sense to reformat your harddrive and reinstall Mac OSX.
This is especially if user error leads to problems with your iMac (or similar), or else you call Apple Support who advise writing over your existing install, leaving various errors with existing applications.
Going back to square one is easy:
1. Insert the first book disk into your Apple
2. Switch the Apple on and hold down C on the keyboard.
3. Follow the instructions that come up
4. Select “Erase and Install” from the installation options
5. Follow the okay the instructions
6. Do something else for a while as the process can take some time
7. Insert disk two to continue the new install and continue
It really is as simple as that. 
And if you had any issues with your previous install, you are now in a better position to take care of them and run your Mac better.