All you need to do is to
# 1
Not just leave your computer on with you signed in. I learned that the hard way. When you leave the computer, click start and change users or log out. Set up a password for your account user name.
Go into Control panel and set up Users and make him a separate user and also set up a user name of guest. Set the user permission you want them to have. Unless you give permission as Adminstrator no one can open any of your files or your favorites except you.
You can ten set up his permissions of what he is allowed to do on ypour computer.
Ed