i think you should search also... but i am bored so i will tell you...

dry: just N2O injected into your intake (normally before the TB)

wet: N2O and fuel injected into your intake (normally before the TB)

direct port: this is, on a four cylinder, like 4 wet kits... it is 4 nozzles that are placed one per cylinder, in the intake runners... obviously you will run a smaller shot on each, but this makes sure that each cylinder gets equal amounts of N2O and fuel...
-Keith