I have really vital documents that have been uploaded onto my computer not to mention the fact that I have used my computer for buys and my name and other vital info is on there. Can anyone please tell me, in detail, how I can permanently erase EVERYTHING that is on my Apple Macbook hard drive and on the computer itself. Can you tell me how I can do it for free? (without purchasing software or anything like that). Thank you, I really appreciate all the helpful answers.