Pi Servo Hat Hookup Guide
There are only a few items of interest on the board, as it is a hat designed to be minimally difficult to use.
USB Micro B Connector - This connector can be used to power the servo motors only, or to power the servo motors as well as the Pi that is connected to the hat. It can also be used to connect to the Pi via serial port connection to avoid having to use a monitor and keyboard for setting up the Pi.
Power supply isolation jumper - This jumper can be cleared (it is closed by default) to isolate the servo power rail from the Pi 5V power rail. Why would you want to do that? If there are several servos, or large servos with a heavy load on them, the noise created on the power supply rail by the servo motors can cause undesired operation in the Pi, up to a complete reset or shutdown. Note that, so long as the Pi is powered, the serial interface will still work regardless of the state of this jumper.
Servo motor pin headers - These headers are spaced out to make it easier to attach servo motors to them. They are pinned out in the proper order for most hobby-type servo motor connectors.