why does the outter part of my knees hurt and whats that tendon called?

Answer 1

Its probably a slight sprain of the lateral collateral ligament. (tendons attach muscle to bone, ligaments attach bone to bone and hold joints together) It could also be the ilio-tibial band which is a band of fascia that runs through that area too. (probably the ligament)

Ice it and rest it, if its still painful after a day or two see a doctor.