While your Mandrake Linux system loads and shows some technical information and a loading progress bar on the screen, we'll take the opportunity to introduce a fundamental concept of multiuser systems: the session.
GNU/Linux is a multiuser system. This means that more than one user can access the same machine, each one with the ability to keep his own data and configuration files private and protected from other users. To be able to do this, different user accounts must be created on the system by the system administrator. The administrator is the user named root, whose password has been set during system installation, and he has access to all files on the system.
The word “session” identifies all activities which take place starting from the moment when a user logs on to the system, up to the moment when the user decides that he doesn't need to use the system anymore.
Starting a session is also called “to log in”. To log in means identifying yourself to the computer; think of it as a security officer validating who you are before letting you in. After logging in, the system takes a number of actions in order to give you access to its resources.
Likewise, ending a session is also called “to log out”. To log out means you are telling the system you no longer need to use it; it closes your personal session, and the resources you were using are made available for someone else.