As a puppy your dog was taught by its mother to greet other dogs face to face by licking each other faces. Unless taught otherwise by you, your dog will think that this is the normal way to greet a human so will try to reach your face by jumping up at you.
A bearded Collie barking at its owner wanting to jump up
Jumping up can also be a sign of dominance. It is important to teach your dog from a young age that jumping up is not acceptable.