Here’s a neat little trick if you want to let a guest or friend use your Mac for something. You can create a guest account. The nice thing about this guest account is that everything the user does will be wiped out as soon as they log out. So no unwanted changes will stick around your computer and they’ll also have the security of knowing you aren’t going to have access to a saved password or account information.
Here’s how to do it. Start by clicking the Apple icon at the top left and choosing System Preferences.
Choose Users and Groups.
Click the lock at the bottom of the Users & Groups window to enter your admin password and log on. Then click Guest user to enable a Guest user.
To turn off the Guest user function, just uncheck the box next to it. Click on Parental Controls to restrict the use of the camera, mail, and app stores or to limit the amount of time user can spend on the Mac.
When the guest user logs out, all of the information in their file will be deleted.