How do it I make a folder with a passcode for certain photos and videos i do not want people to see

Mac OS X is inherently a Multiple-User system. If you create only one User, it operates no differently. User data is protected from other users' access by the permissions system. By definition, each entire Account is locked from access by others.

So step 1 is to give each other User their own account, and make certain that the folder you want kept private has Everyone='No Access' permissions.

Then stop automatic Login on your account, and enter your username and password each time.

The next step is to insure that others cannot casually use your Account. You do this in the Privacy pane, by setting a very small time before the screensaver activates, and the screen LOCKS, so that only a User with your password can clear the screensaver and see any of your files. If you wander away from your computer when you are logged in, the screen will promptly lock and allow no access for others.

If you have given out your password to everyone, then change it and do not share the new password with others, give them their own account information instead.