Handy post from Circuit Basics.
Sometimes it’s difficult to keep track of all the useful Raspberry Pi commands you use, so I created a list of some of the most common and important ones that will make using Linux on the Raspberry Pi a lot easier.
There are two user “modes” you can work with in Linux. One is a user mode with basic access privileges, and the other is a mode with administrator access privileges (AKA super user, or root). Some tasks cannot be performed with basic privileges and you will need to enter into root mode to perform them. You will frequently see the prefix sudo before commands, which means that you are telling the computer to operate the command with super user privileges. Another way is to access the root command prompt, which operates all commands with super user privileges. Access root mode by entering sudo su at the command prompt. After entering sudo su, you will see the root@raspberrypi:/home/pi# command prompt, and all subsequent commands can be entered without the sudo prefix and still have super user privileges.