There's a real limit to what you should do yourself here, and it's not about skill - it's about what's under tension. If a panel has popped a roller but the door is otherwise hanging level and the springs look intact, you can often close the garage, unplug the opener, and wait for a tech without making it worse.
What you should not do is try to force the door back onto the track yourself, especially if a cable has come off the drum. A door on torsion or extension springs stores a lot of energy, and a door that's already off one track can shift again while you're working near it. That's the honest limitation on this page: we can walk you through what to check by phone, but we can't talk you through re-tracking a door safely, and we're not going to pretend a five-minute YouTube fix applies to every case.
What's safe to check yourself: the track for obvious dents or gaps at the wall bracket, and whether the door came off because something hit it versus coming loose on its own. Either answer helps us bring the right part.