ADB, or Android Debug Bridge, is a command line tool included in the Android SDK that allows users to control Android devices connected to a computer. It can install and uninstall apps, copy files between a computer and device, run shell commands, and more. To enable ADB, users must download the ADB tool and USB drivers, enable developer options and USB debugging on the device, and connect the device to the computer with a USB cable. Common ADB commands include pulling and pushing files between a computer and device, installing and uninstalling apps, and opening a shell to run commands on the Android system.