The easiest thing to do is to not let others use your account, and require logging into it. Then also for the folder of interest, restrict who can read and write to it. You'd do that by performing a 'get info' on the folder and changing the "Sharing and Permissions to just your account. The 'staff' account you may see would include any account set up as an Administrator.
A more difficult way would be to create a disk image that requires a password to open it up for use and set up some linking to it. I'm not sure I want to figure the technical details out for you. This trick, if doable, is complicated for the novice.
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