Depends what sort of booster it is? did they come together?
Normally you would have one with a lan cable plugged into a wall socket next to your router,then a lan cable from that into your router, then another plug that you plug into a power socket some where else in the house and the two boxes talk to eachother using your electrical wiring.
Or if its a wifi repeater then its just a box on its own that you plug in to a wall socket, but in range of the router.. so it can pick up and amplify the wifi signal.
Hi, I have not seen the ones Virgin supply but if its two then I would assume one goes by the router with a lan cable from the router into that plug, then place the other one some where else in the house where the wifi is weak and that will act as another wifi point.