what parts of a paintball gun do i have to oil?

For the Spyder Xtra, remove the barrel, place a few drops of oil in the asa (where the tank screws in), screw the tank on (make sure it's filled), and dry fire a few times into a towel (dry firing = firing without paint). This circulates oil around the internals, so you don't have to specifically lube anything. Removing the barrel makes sure no oil gets in the barrel, cuz it'll mist out a little bit in the beginning while you dry-fire.

You don't need water on anything unless there's a ton of paint and dirt on it. Just run a squeegee through the barrel and wipe down the gun with a rag whenever it's dirty.

Every so often, maybe every 2-3 months, depending on how often you play, you'll want to completely disassemble the Xtra to clean the internals. Just need to wipe down parts with a rag, apply a couple fresh drops of oil to all the o-rings, and reassemble.