Reformat

I am very new to Mac. I recently purchased a MacBook Air and I installed programs that I do not want and aren't working as expected. There are files that have replicated themselves to iTunes instead of just using the directories that they were in like my PC. I would like to reset it to the way it was right out of the box. I tried to the command +F at start up but I am unsure which option to use. There is an option to use Time Machine but I didn't make a backup there but there is an option to install a new operating system. There was always a restore partition on all of my PC's to wipe it out and start from scratch again. Does anyone know how a I can do this?