DIFFERENT PRIVILEGES FOR DIFFERENT USERS

UNIX systems have built-in security features. Most users cannot set up a new user account nor do other administrative procedures.
The user root is a special user, sometimes called a super-user, which can do anything at all on the system. This high degree of power is necessary to fully administer a UNIX system, but it also allows its user to make mistakes and cause system problems. For this reason, the user should set up a personal account for himself that does not have root privilege. Then, his normal, day-to-day activities will affect only his personal environment and the user will be in no danger of causing system-wide problems.
In a multi-user, non-personal environment, the user is most likely to have only user, and not super-user privileges. This security is even more important when more than one person is involved because one mistake by the root can affect every user and the entire system.
UNIX also has security to help prevent different users from harming each other on a multi-user system. Each user owns his or her environment and can selectively let groups or all others have access to this work. If the user is doing private work in one area that no one else should be allowed to see, then he should restrict access to the owner (himself). If the user and his team members are working on a group project, he can restrict access to the owner (himself) and everyone in his group. If this work should be shared with many or all people on the system, then he should allow access to everyone.
LOGGING OUT
When the user is done using the system, he should log out to prevent other people from accidentally or intentionally getting access to his files. The normal way to log out from almost any shell is to type exit. This causes the shell to exit, or stop running. When the user exits from his login shell, he logs out. Some shells, depending on the configuration, will also log the user out when he types the end-of-file character, typically Control + D.