It woks by magic.
It is driven by the starter motor, running off the battery. You probably won't be going miles, so you'll not flatten the battery, whilst the alternator is kicking out juice anyway. Nor will you overheat / burn out the starter motor, unless you are a numpty.
Start the engine. Put into neutral, leaving the engine running. Push the 'R' button. Despress the starter button, the bike will move backwards for as long as you depress the starter button. To stop, release the starter button, though the bike will continue backwards for little bit. Repeat at will, until you get the bike where you want it. To disengage, push the 'R' button again or just turn the ignition off.
it is maybe slightly unnerving at first but you soon get used to it. I haven't yet been brave enough to try a full 'feet up on the pegs' reverse, though I may yet. I feel though that it might not end entirely well.