In my arm where my veins are its painful when i move. i just want to know why does it hurt?

This is a little: difficult to sort out without talking with you in person. It would be very unusual for vein problems to be causing pain in your arm. Much more likely the muscle underneath is sore but what you can see is the veins. The pain most likely if from a strain/overuse: lifting, carrying, playing arm-related sports, etc. Put an ice bag (of peas!) over the sore spot; talk to your Doctor if persists:)