Mainly by ADB, you can do things like: Debugging your Device and Unlocking your device bootloader. Most users use ADB just to have an Unlocked Bootloader and install Custom ROMS and Custom Recoveries like twrp or Clockwork. ADB Install Process is simple. Follow these steps and you are good to go.
ADB Install Process
Step 1: Download ADB Installer From here. DOWNLOAD
Step 2: Install it as a normal software. Go through the screen and select Yes each time.
Step 3: Enable USB Debugging in your Android Devices. Guide Here
Step 4: Go to C: and find adb folder. Holding shift Right in the folder. Select Open Powershell or CMD here.
If you are a Geek who is interested in Mobile stuff, then you may have used Some Commands like adb devices, Fastboot devices, adb reboot, Fastboot reboot etc.