I feel real pain in my right knee, as if it is bruised, can you tell me what might it be?

it could possibly be a strained ligament. if you stay off of it and rest it as much as possible that would be the best thing for it. there isn't many things you can do for knees as far as stretching goes. you should ice it in 20 minute increments and then let it rest for half an hour. you can also try applying heat for the same amount of time. if you need to go somewhere like school or to the store or somewhere that you can't rest it you should wrap it or get a knee brace. i hope it feels better and if it doesnt start getting better within two or three more days then you might want to go to the doctor to get it checked out. good luck :)