In addition to the above excellent answer, I offer some other problem areas when removing rear drums. Some may pertain to one auto, but not another. This is just general infromation I hope you find useful.
As stated above or below, (not sure where this comment will be placed) find the adjuster for the brake shoes. In my Cavalier, there is an oblong hole on the backside of the drum plate with a rubber insert to prevent debris gaining entrance. Revove if present, and use a wide screwdriver or preferably a brake adjuster tool. With screwdrivers you run a greater risk of stripping the teeth/gear on the adjuster itself leaving no way to adjust the shoes wihout removing the drum, which is what we are attempting to do in the first place. Once the teeth on the adjuster are stripped, and the shoes are stuck in the groove inside the drum, there are only two ways to remove the drum. Brute force, as I was able to do on mine, or use a grinding tool, and cut the drum off. The later solution is a last ditch effort, and one a proffessional shop would likely use instead of brute force muscle. A brake adjustment tool at 5-$10 is a great investment. When adjusting the shoes inward, which is what we want if the shoes are stuck in a groove. This happens a lot when people such as myself wait, and find themselves running metal to metal, creating a groove. On my vehicle you must use two tools. One pushes the brake adjuster arm away from the star wheel so you can turn the gear/starwheel which backs the shoes inward. A good way to ascertain which direction to turn the starwheel would be, insert a scredriver or tool, and turn the starwheel. When you here a click, the shoes are moving outward as the click sound will inform. You now want to use both tools, pushing the arm that rests on the starwheel out so you can insert the brake tool, and move the wheel in the opposite direction, backing the shoes off.
If your problem is a rusted on drum at the point of hub/bearing contact then hit the face of the drum (STAY AWAY FROM THE STUDS) with a good size hammer. Should this not break the rust connection, then spray penetrating lubricating oil around, and inbetween the drum and hub. Let it sit for an hour, then smack with a hammer again. If this doesn't loosen the drum/rust, repeat the above, and try again. Don't use too much force when hitting the drum as you could damage the bearing. However, you can whack it fairly hard, and in fact, I used a medium hit with a 3' sledge hammer/axe combo. Two hits and the drum was off, just don't use excessive force unles required, and know you may damage the bearing, not likely, but possible. The main ingredient here is the penetraing oil, it really does the job for you if with time and patience. This could take a full day of repeated use every hour on the hour until the rust gives way so be prepared. WD-40 may work for some, but you may need something stronger avaiable at your local auto parts store. I don't have the can I used so forget the name, but buy a can that states it is penetrating oil, and you'll be good to go. Hope this helps someone, worked for me, but I hit stud, and had to replace which is why I stated stay away from the studs. I am fairly certain I also read some proffessional advice on this which stated to hit the face only, not the sides. either way, if using a sledge, with a medium hit, you should be fine.
Another option is easier, but more difficult to find as purchasing this tool is expensive. Use a brake drum puller sometimes available for lend at your auto parts store, but I have not located one, and live in a very large city so good luck to you, and hope that drum comes off easier than mine did.