I have a 13" MacBook Pro that Apple has lent me while my new 15" is being built and I need to restore it to the same condition as the day I received it from Apple. How do I do that?
You can do that by shutting down your computer, then when you turn it on press and hold command+option+R and wait a while (normally about 5 mins)
Once your in Internet Recovery go to
disk utility and format your drive. After you have done that go to
Install OS X and follow the instructions. This will create an clean install. Once you do that shutdown the computer and then you can give it back to them. Don't do the setup.