Drive belt

This is considered too basic to bother with a video. There should be a belt routing diagram on a sticker on the engine or somewhere under the hood. If the belt popped off, there is a reason that happened. That has to be addressed first. There is a spring-loaded tension-er pulley that could be weak. More commonly one of the pulleys is tipped, turned, misaligned, or wobbling due to worn bearings. Usually you can identify which one is causing the trouble by wiggling them by hand.