This PCB lets you plug four HUB-ee wheels into one controller for synchronous drive (i.e. all the wheels plugged into this PCB will get the same control signals). It also isolates the quadrature encoder channels of each wheel and routes one set through to the controller whilst making all the quadrature and standby pins for each wheel available on pin headers.
There are a set of power input pins for supplying power and some power capacitors to smooth things out. You can connect it to a controller using a Micro-MaTch connector, or a standard 0.1" pin header.