What is adb?
adb stands for Android Debug Bridge. In short, it’s a tool that provides you the ability to manage your android device through a console on your computer. With adb, you can execute shell commands on your device & copy files to/from it.
Open a CMD Prompt (or terminal on linux/mac), and cd into your sdk directory/tools. Type adb, and it will output a list of available commands. There are a lot of options/commands, but I’ll outline a few of the most common here. Since android is linux, most of the commands you would expect are there when using the shell (ls, cd, cp, mv, rm, etc).