This is a very simple, straight-forward system. First of all, don't try to get the drum off by prying on it. It is held to the hub by the lug nut studs. Remove the center cap and cotter pin, then remove the nut and outer bearing.
Basically, remove the springs and hold-down hardware, then put the new shoes on the same way. Just take one side apart at a time so you can compare to the other side if necessary. Be sure the drum will go on before you take the second side apart.
The shoe with the shorter lining goes toward the front of the van. For the self-adjuster cable, be sure the guide shoe is seated in the hole in the shoe. The hook on the return spring will hold it in place. Watch closely how that hook comes out because a lot of people try to put it in wrong.
Note that the shoes each have three "lands" where they ride on the backing plate. You'll likely see some grooves forming where those lands have been sliding back and forth. Put a light coating of high-temperature brake grease on those six spots to prevent more wear and to prevent that annoying squeak when you release the brake pedal.
When you're done, both shoes must be touching the large anchor pin on top, and you must be able to push the parking brake strut bar a good 1/8" against the anti-rattle spring pressure. If you can't do both of those things, something is assembled wrong, or more commonly, one of the parking brake cables is rusted tight in the partially applied position.