From Black Desert Wiki
Players in Black Desert can ride on mounts to travel across the vast lands. There are also mounts for siege, and trading. It's unknown how many types of mounts Black Desert will have. They have only shown three kinds.
In a Q&A with Pearl Abyss's development team, horses have to be put into stables and can not be called from the field. Horses have the ability to "drift" when making turns.
Horses can also be use to charge into the castle during siege warfare.
You might also be able to equip Carts to them, but not much information is known.
During siege warfare, Elephants can be use as mounts to offensively attack players. Ranger classes can fire their bow and arrow from a top the elephants.
The Tamer class has a unique mount which can be used to attack monsters and possibly other players. The mount does not need to be stored in a stable and can be called upon at will.
Some or all mounts can be breed. No further information is known.