Welcome Sidecar,
For the 500, there are two pots, so I'd be shocked if both of them have gone out, might be something else.
Yes, the only heat source is the pellets themselves. There is an electrical plug at the bottom of the firepot. First clean out the pot, looking for any old ash that has compacted around the ignitor.
IF it is covered with ash, that may be your problem.
IF it is NOT covered, then you'll need an ignitor.
The good thing is you don't "have" to have an ignitor. I know people that always manually start their smokers once the ignitor goes bad. Starter jell like Nordy says or a blow torch (works for me). Once you have a solid fire, then you'll be okay.
There are a # of lessons from other owners. The main difference is to learn the differences between the 500 and 100's.