Note: to create or delete users, you'll need to be an administrator or know its password.
Type "add user" in the start menu and click "Add or remove user accounts".
Click the "Create a new account" link in the Control Panel (bottom left, below list of users).
Type the "New account name", without using special characters: /\[]":;|<>+=,?*
Leave "Standard user" selected: they will be able to do most everything, but will need to enter an administrator's password at UAC prompt for potentially dangerous operations.
Or select "Administrator": that user will be able to change and access anything on that PC.
Caution: if a user's profile becomes infected, the virus has the same privileges as the user.
Click the "Create Account" button: Windows 7 will add standard folders for that user.
Click on that new user's name / icon, and select "Create a password" on the next screen.
Enter and confirm the password, type a password hint, and click "Create Password".
Fiddle -or not- with other settings on the new user's screen, and close the Control Panel - that person can now start using Windows under his/her own profile.