Hello Tony
It is very important that the two nipples are greased regularly. You will need a fairly powerfull grease gun.
Lift rear of vehicle off road (takes pressure off the joints) attach grease gun to nipple and pump untill you see grease coming out of joint at the wheel end of the axle, it is very visable you cannot miss it. If the joint has not been greased for a long time you have to pump quite hard, you will then hear a cracking sound as the old grease if force out. Pump untill clean grease flows out.
Dave B