It is a little mini-shield kit that lets you attach Digispark shields to the DigiX - many of you have these little shields and they're super useful when you need to add say one relay to your DigiX project.
There are two jumpers on this mini-shield. One is to select the power for the shield. ie. 3V if used with a DigiX or Arduino Due, and 5V if used with an Arduino Uno.
The second jumper is for setting P0 as either the SCL1/D70 pin or D8 pin. Set the jumper in the D8 position if you need to power something that needs more than 3mA.