With the handwheel clutch tightened, does the machine turn freely? Does the needle bar move up and down when turning the handwheel by hand?
With the handwheel clutch loosened, does the handwheel spin freely on the shaft? Does the needle bar move with the handwheel clutch loosened while turning the handwheel by hand?
When operating the pedal, does the large pulley move freely?
If the machine turns freely with the clutch tightened, and the pedal moves the large pulley freely, then put the belt on, sized correctly (hopefully Janey will post the link about sizing a belt, but you should be able to find that easily). When you are ready to start operating with the pedal start the machine with your hand turning the handwheel towards you from the top (counter clockwise when looking at it from the handwheel end of the machine). I have owned only 3 treadle machines and on all 3 I had to start the machine moving with my hand, not just trying to push on the pedal.
If you make it this far and have cloth under the presser foot, the cloth should move away from you with the handwheel moving counter clockwise; if the cloth moves towards you then the machine operates with a clockwise spin.