Can you hookup a compressor and a nail gun at the same time?Or is there only 1 input?

not with the standard valve assembly-- yes with a valve combo

taking a general stance, a nail gun will typically either be powered by compressed air from an air compressor, or electrically (a handful run off battery packs). If using a pneumatic nail gun (air powered), then it will need to be hooked up to an air compressor. An electric Nail gun will need only a charge (battery powered) or a power cord to be plugged into a receptacle. A pneumatic nail gun will not operate without an air supply, so a refillable air tank or an air compressor is required. You would run one or the other, not both as there is only one input on the nail gun. An air compressor would eliminate the need for a separate tank, but a small portable tank would be handy if you have to keep moving away from your compressor.