Not much you can do for one except rest it and let it heal. They're kind of like a sprain in that they hurt nearly as much as a break does.
My dad coached basketball and his players were getting jammed fingers all the time. He said it was the most common injury for a basketball player because the ball can take a bad bounce, or the player misjudges the trajectory during the game and makes a grab for it at the wrong time. It was just part of the game, but I know it had to hurt to keep playing with a jammed finger. Sometimes, the players would fib about their fingers being jammed so they could stay in the game.