What Did I Do To My Elbow? I Smashed My

What did i do to my elbow? i smashed my elbow against my locker door. The tip of my elbow hurts when something gets in contact with it. i can't straighten my elbow. the tip of the elbow is also red. and too me but no one else in my family can see something different on that elbow than the other. I am 15 years old, i weigh about 82 pounds and my height is 4 feet and 8 inches. I have no medical history because i am adopted and there wasn't any information given. thanks for your help.