Command lines simply put, are shortcuts used to execute specific functions. For example if I am using a Windows based system. I could use cmd to open the command prompt. Then I could type out a specific function to. For example, scan a drive and see how full it is. Or defragment that drive. Another example I could use is. ipconfig this would show me all the data related to my network and my connection. This gives me access to my IP address. Which then could be shared or used to create locally hosted servers from my PC. Say for, Game servers if I wanted to host for some friends. Instead of using a Peer to Peer connection. I could also keep this server on so long as my system is on. Instead of having to have the game application running. Using chkdsk can be used to show the health of a certain drive. Which can be used in conjunction with a disk path to specify which disk you want to check.