CISCO IOS CLI and command modes

The Cisco IOS command line interface (CLI) is a text-based program that enables
 the entering and executing of Cisco IOS commands to configure, monitor, and maintain Cisco devices.
Almost All  CISCO device use similar CLI,  When the router has completed the power on sequence, and the Router> command appears, that Initial mode of  All the CISCO Device, that we call User Exec mode,
Now CLI can used IOS command,  this mode used to enter privilege mode, monitoring some status, network connectivity(ping, traceroute), lets move to next Mode by typing  enable and hit enter.

Router>enable

Router# !wellcome to Privilege Exec mode, many command available used such as Monitoring, debugging, configuring, configuration saving, and much more.  type configure terminal or conf  t  goto gobble configuration mode
Router#conf t 
Router(config)#!this is a primary Configuration mode, Almost 99.99% Command for a configuration, 
Router(config)#!Other modes are sub-configuration, 
Router(config-if)# ! Interface configuration,
Router(config-router)# !Router configuration,
Router(config-line)# !  terminal line confuguration,
basically i have discussed about 4 CLI modes, those are User Exec, privilege mode, gobble configuration,
and Sub-config mode as below image.