If you want to let someone use your Mac but not have access to all your files, Guest User accounts can come in handy. Depending on your installation, guest accounts might be disabled so you see just your name on the login screen.
But you can setup a guest account easily (about two or three clicks!). You'll need to be one of the administrators to enable the guest account.
Here's How to Enable Guest User Account on Mac
Step 1: Click on “Apple Menu” and then choose “System Preferences.”
Step 2: Now, click on “Users & Groups.”
Step 3: If you have a Mac password setup, click on the “lock” icon at the bottom of the screen. Enter your password. This will unlock the settings (so you can now edit them).
Step 4: Click on Guest User from the sidebar showing the user list.
Step 5: Check “Allow guest to log to the computer.” (Enable it).
If you happen to logout now, you'll see a Guest account at the login screen. Clicking this will unlock the Mac but will keep the access to a bare minimum. The “guest” can use Safari and a few other apps but won't be able to view your files/folders.
If you notice, the User & Groups preferences has a few options for the Guest user. One of them is parental controls: you can enable it (tick the checkbox) and then configure the parental controls by clicking on that button labeled Open Parental Controls.
If you want to the guest user to be able to access just your shared folder (/User/Shared), check the Allow guests to connect to shared folders. This will let the guest user access shared folders.