Hi Jamie.
When using the hose, slip the free end of the rubber yellow thingy, which is attached to the hose, over the yellow hook attached to the lower body of the machine.
Its to stop you tipping the machine over, through tugging on the hose too much. By attaching the rubber bit over the hook, you move the tugging force closer to the ground, soooooo when you tug on the hose you merely pull the machine around with you, rather than pulling the machine over on its side.
Something like that anyway. Hope it makes sense.
Paul