Most pool pumps are 'self priming'. Pumps specified for in-ground pools are self priming. Pumps specified for above ground pools may not be self priming.
The difference is because it is assumed pool equipment for in-ground pools are at or above the water level. Water will not naturally flow from the pool to the pump. The priming is the replacement of air in the suction pipe with water. A self priming pump is built to suction the air for a limited period of time until it gets the water flowing.
With a above ground pool the equipment will be below the waterline and if the pipes are not plugged or closed with valves water will flow into the pump before it is even started. An above ground pool pump does not need to be built to suction air as it starts.
A self priming in-ground pool pump can be used in an in-ground pool or above ground pool. If a non-priming pump designed for an above ground pool is used in an in-ground pool where the pump is above the water then the pump must be primed when started.
Priming the Pump
You can dump a bucket of water or run the hose into the pump basket if you like, then replace the lid after cleaning and lubricating the gasket with Pool Lube, secure it tightly, and then start the pump. It should prime in a minute or so. Especially if your pool equipment is not more than a foot or two above the pool water line. Be sure to have your filter relief valve open until it shoots out water.
Depending on how high your equipment is off the ground and how long your suction line is you may find that any water you put in your pump basket will just drain back into your pool. In that case, close up the pump lid and rely on the self priming of the pump.
Reasons a pump loses its prime
One of the most common reasons a pump loses its prime is the pump lid gasket. Sometimes, they will seal well under suction but after the pump is off, they don't seal as well so leak air in. Other possibilities are the pump drain plugs and filter. After turning off the pump, listen close to the filter to hear any bubbles rising up. Otherwise, lube the lid and drain plug gaskets with pool lube and see if that helps.