Hi Ashad

from your description it would be impossible to know what you have injured. These are the most likely injuries

1. you may have torn one of the collateral ligaments. These are the fibrous bands that bind your thigh bone to your shin bone on each side of the joint. Is the pain on the inside or the outside? this may indicate which one
2. You may have torn one of the Wikipedia reference-linkcruciate ligaments There are two of these cords of fibrous material that lie deep inside the knee joint. The stop the two bones gliding and rotating too much while allowing the normal movements to occur. The Anterior Cruciate Ligament is the most common injury.
If you tore one of your ligaments initially this may mean your knee joint now has too much slippage in the joint and has become a bit unstable - therefore prone to reinjury
3.You may have torn one of the menisci - the crescent moon shaped cartilages the sit in your knee joint and improve the mechanics of the joint. a torn medial Wikipedia reference-linkmeniscus goes hand in hand with a torn medial collateral ligament.

However you could have done something else. While I could ask you a whole lot of questions to try to narrow down the problem what you really need to do is get your knee properly checked out by a sports or Musculoskeletal phyiso. At this stage you should probably have an Wikipedia reference-linkMRI done (or some other relevant image technique) to have a look what is torn.