Why does knee hurt to straighten it out hurts when bent it hurts also when i get up and walk putting pressure on it and if i stand too long it swells?

Effusion: It sounds like you have a knee effusion. An effusion is a collection of fluid within the knee joint. It increased the pressure within the joint. As you extender/flex the knee the increased pressure will cause discomfort and pain. The effusion would also caused swelling. There are many causes for a knee effusion. This would clarified by a visit with your local MD to determine what's going on