Water gun is a move that makes the user shoot rapid balls of water towards its opponent. It isn't very strong even when a lvl 80 uses it on a lvl 20 or 10.
WaterPulse is a move that creates a water shield around you whilst the User shoots sparkly balls of water. It is a very strong attack.
Whirlpool is a move where your opponent must be in VERY close range. Your user must be next to your opponent when using the move as your character spins and makes all the pokemon trapped in his whirlpool shoot away in different directions making them get stuck sitting down. It is a very effective move.
Wailmer evolves into the event pokemon Wailord