While you can restrict access to your user account on your computer by setting up a password, you can also restrict specific folders from being opened by secondary account users on the same computer. The folder's settings that allows you to lock the folder can be found in Windows Explorer on your Windows PC, or can be found in Finder on Macintosh computers. Once locked, any user who attempts to access the folder will be denied access until you remove the lock.
Lock folder on a Windows PC
Double-click the "My Computer" icon on your desktop, and double-click the "C: Drive" icon.
Locate the folder you wish to lock, and right-click the folder's icon. Click "Properties" on the shortcut menu.
Select the "General" tab, and click the "Advanced" button in the lower-right corner of the window. Click the box next to "Encrypt Contents to Secure Data."
Select the "OK" button to save the changes and encrypt your folder.
Lock a folder on a Macintosh computer
Click the "Finder" icon on your screen's dock, and click the "Macintosh HD" tab under the "Devices" section in the Finder's sidebar.
Double-click the "Users" folder, and double-click your name to access your account's folders.
Right-click the folder you wish to lock, and click "Get Info" from the shortcut menu.
Click the box next to "Locked" in the "Get Info" window to lock the folder.
Click the arrow next to the "Sharing & Permissions" section of the "Get Info" window, and click the arrows underneath the "Privileges" section.
Select "No Access" from the drop-down menu to restrict access, and click the red button in the upper-left corner of the window to save the changes and close out of the window.