The clear plastic cup goes over the breast, with the nipple in the center of the shield. Then, following the instructions, you either begin pumping manually or turn the pump on. For premature babies, the milk should be pumped every 2 hours or so, with every 3 hours usually recommended at the maximum amount of time between pumping. Pumping your milk may not be enough to get your milk started. If this is so, a lactation consultant is a wonderful person to ask for help.
Most insurances cover the cost of a lactation consultant.
The La Leche League is a good place to find consultants. Also, your local hospital can often suggest one for you. If you need a little help producing more milk, there are herbs out there that can safely help. Of course, as always, before starting taking any herb or medication, consult your doctor. Fenugreek is one herb that increases milk supply.