You can attach one G8 expander to a DROID master. It will give you eight additional jacks. Each can be used as a gate input or output. This means that - other then the master - it does not input or output continous voltages. When used as outputs the jacks output either 0V or 5V and can be used to trigger other modules.
In your DROID patch the jacks are addressed via G1, G2, G3, ... G8.
Shipping includes a short ribbon cable for connecting the G8 to the master.