When you pull the pull stater, the centrifugal force acts on the pawls in the mechanisim. They swing out and engage a sprag clutch of sorts and that's how you turn the engine with the rope/spin the engine over. Once the engine is turning, it free wheels over the sprag clutch. That's why once the engine starts if you keep the rope out you hear that sound (ratcheting).
Did that help, or were you happy when you thought it worked by magic?