Question
I have a system with shallow well for sprinkling only.  Keep loosing the prime.  It takes about 5 minutes to prime it. All water drains out of pump right after shuting off. Several people have told me it might be the check valve. What exactely is a check valve and how does it work.  No knowledge what so ever of this type of thing.

Answer
A check valve, or foot valve, is a valve that is on the downstream side of your pump, (usually at the bottom of the suction line in the well), that keeps the water from draining out of the line when the pump is off.  It sounds like you have a problem with this valve.  You would need to pull the suction line out of the well to have it checked.  I suggest having a well service person do this for you, unless you or someone you know is knowledgeable in the proceedure.