If you are a Network Administrator, you are very much familiar with user mode and enable mode of Cisco IOS shell. When a user access the Cisco IOS shell, initially he/she access the device Shell with a privilege level of "1". From user EXEC mode, a user cannot change the Cisco Router's or Switch's configuration settings or he/she cannot view the running configuration file. The user may view the status of interfaces or routes in the routing table if the use is at user EXEC mode (Privilege level 1).
The use can escalate his/her privilege level to 15, by entering the Cisco IOS command "enable" from user EXEC mode.
In Cisco IOS shell, we have 16 levels of Privileges (0-15).
Privilege level 0 - No Access at all
Privilege level 1 - User Mode (also known as "user EXEC" mode)
Privilege level 15 - Privileged mode (enable mode or "privileged EXEC" mode)
Remaining 2-14 Privilege levels are available for customization.
A higher privilege level has access to all Cisco IOS CLI commands which are available with lower privilege levels. In other words, the Cisco IOS CLI commands which are available in user EXEC mode (Privilege level 1) are a subset of the commands that are available in privileged EXEC mode(Privilege level 15).
Click the following link to learn How to configure multiple Privilege Levels Cisco IOS CLI Shell