If you want to restrict other people from being able to access a file or folder you want to change the security permissions for said file or folder.
This is what you want to do:
1.) Right click the file or folder and go to 'Properties'
2.) Click the 'Security' tab
You will see two boxes here, the top box will list everyone that has permissions to the folder. The bottom box will show what permissions the currently selected user has to that folder (Ex: Full Control, Modify, Read, Write, Special). Underneath the first box you can click 'Edit' and modify the permissions. Once you are here, do the following:
3.) Highlight user you want to change the permissions for (If you don't want the user to have any permissions to the folder or file, click 'Remove' with the users name highlighted)
4.) Change permissions as needed
Be careful when changing permissions to a folder or file! Do NOT change permissions on system or program files unless instructed to do so by a program or trained technician, if you make improper changes to permissions it can leave programs and files inaccessible. For example, if you remove yourself from the permissions on a folder or file, you will not be able to access the file to do anything.
Also, it's not recommended you remove the admin account from the permissions. In the event anything goes wrong you will be wanting that account to login and fix the problem.
Hope this helps!