Sharks are hostile Mobs that are found swimming around slowly in water. When the player enters the water the Shark will turn on them and swim very fast in order to chase you down and attack you. Sharks have a rare chance of dropping a Shark Egg when killed, but most commonly drop Shark Teeth, which can be used to craft Chainmail Armor (as seen here), and a Shark Sword.
Sharks have a 10% chance of dropping a Shark Egg when killed. In order to get a tamed Shark, you need to hatch this egg by throwing it into the water, which will hatch a friendly baby Shark. Once it grows big enough, it will attack other Mobs (like Squid). Tamed Sharks will not attack other Sharks or the player.
You cannot ride a Shark.
There is no current way to heal a tamed Shark by "feeding it" (as is possible with other tamable Mobs). The only way to heal a tamed Shark is to throw a Splash Potion of Healing at it.
Sharks drop Shark Teeth when killed, which can be used to create Chainmail Armor without the use of Fire or spawning it in. They can also be used to make a Shark Sword, a weapon unique to the Mo' Creatures Mod.