The suction side (the side with the clear plastic filter) should go into the fresh water tank to let the pump draw water.
The outlet side should go to a cold water line.
add edit: before taking time to plumb it in, check to make sure it works. If it is the original pump it is likely that the diaphragm is cracked.
2014 Silverado 1500 5.3L maximum trailering package (yes, I'm towing the 34')