I have a shed that has 2 plug outlet that needs replacing. I imagine the box inside is OK, so would I just replace the outlet with any outlet or do I need some special type. I am pretty sure it currently does not have any GFCI on the one I am replacing. Do the outlet covers come separately or are their special outside outlets for this purpose? This is a 15 A circuit.

I laid out a few wires in my backyard (underground feeder UGF wire 15amp 14 2) last season. All wires were put inside conduit which were then put inside the ground like some 18 inches below as suggested in many forums. When I connect those outdoor lights to the outlet which is GFCI enabled, it trips as soon as I plug it in and therefore lights don't turn on. However, when I pluged it in a non gfci receptacle to test the outdoor lighting connections, there is no issue and the lights are operational as they should be (much to my relief). Although, I'm concerned about them not working when connected on a gfci receptacle which is how I'd like to connect given that these are outdoor connections. Anyone has any idea what's the fix here or what's going on. It will be a nightmare (almost impossible for me to dig the ground back up and check the cables for moisture if that's any potential reason ... etc.) I have connected many other things (extension cord, leaf blower etc) on the same gfci outlet and it never trips. It only trips when I connect my outdoor lighting that I installed. Thanks in advance for your inputs.