How Do You Get The Computer To Work In Popotropia I Want To Erase Everything I Put On My Computer So That It Is In The Manufactured State. How Do I Do It.?

I want to erase everything I put on my computer so that it is in the manufactured state. How do I do It.? - how do you get the computer to work in popotropia

I want to leave everything except the things that came with the operating system, but do not know what to use.