how do i reset my macbook to factory settings?

I think i have erased some things that i shouldn't have. I cant restore information on the time machine. It is off, but when i try to cut it back on, it wouldnt let me. Another this is that i did something to the toolbar and its not to factory settings. Some one please help me on this one. i dont know what i erased but i think i erased something i need that wouldnt let me save data.