How do you move airplane backward on runway?

Aircraft are moved around on the ground by ground vehicles collectively known as 'tugs' which typically connect a towing bar to the front landing strut and pull/push the aircraft until it can use it's own engines to manoeuvre. This is typically when the plane is being "pushed back" from the gate, although there are some airports (EWR - Newark) with selected gates so close together that arriving aircraft have to be towed to the gate.