Whales swim by moving their tail flukes up and down. To make a whale's tail put your hands out in front of you, palms facing out. Lock your thumbs together. You've just made tail flukes. Move them up and down.
Fish swim by moving their tails side to side.
To make a fish tail, put your hands out in front of you, palms together. Now move them side to side. Stingrays swim by moving their pectoral fins up and down. These fins are on the sides of their bodies. You can be a stingray by moving your arms up and down.