Directly after flying your broom at the start there is a short cutscene where Ron and Hermione discuss what to do with some old cauldrons left behind by Fred and George. Simple cast Wingardium Leviosar on them (instructions on on-screen command) then flick the right stick upwards twice quickly to flick the cauldrons into the nearby pond. Rinse and repeat on following cauldrons and then Ding, 10G!