Have you removed the drum and nipple from the barrel? You oughta take care of cleaning those out first. Now check inside the vent where the drum was screwed into the barrel. If all CVA's are the same, it'll be a chamber in the breech about 22 cal. in diameter. It may be full of fouling or lube. If dirty, clean it out using whatever you got that'll get down there. Make sure to dry it all out after.
Now that you have it all cleaned a back together, place a cap on the nipple and hold the gun up to a piece of paper or blade of grass. They should bend when the cap goes off. That means all the fire channels are clear.
You didn't mention what caliber you're shooting. If it's a fifty, you'll need 490round balls and some .010 patches to start. If you can find it, get some Goex 2f. I just happen to use 2f in everything from 38 spec. to 12 ga. and in all my flint and cap locks. Just makes life a little simpler for me.
3f will work as well and is probably the recommended grade.
Just to start, measure out about 30 grs. of powder by volume. Get a brass "BP" measure and set it to 30. It'll drop what you need. Pour the powder down the barrel and give it a slight bump. Remember that smaller hole at the end? This'll make sure powder gets all the way down into it. Sometimes the powder will "bridge" and won't get all the way down. Now get a patch and place it over the muzzle and place a round ball in the middle. Using a short starter, ram the ball down. Now get your ramrod and finish the load, making sure the ball is fully seated on the powder. Oooops. First thing. Run the ramrod into the empty gun and see where it stops. Mark it with a pen, marker, tape or what have you at the muzzle. When you run the load, the mark will be about an inch from the muzzle. This gives you some reference as to where the ball seats on the powder. Now that you have the powder and ball loaded, pull the hammer to half cock and seat a cap. Point it down range, pull the hammer to full cock and prepare to get addicted!
Some tips. Keep some Ballistol/water mix, about 1 to 10 handy for swabbing out the barrel after every few shots. You'll notice the ball getting harder to load. You don't have Ballistol? Heck, use Murphy's Oil Soap and water ro just plain water and dish soap. The key is the water to help dissolve hard BP fouling that will build up inside the bore. Also, you can lube the patch with Crisco, tallow or some other non-petroleum based concoction to help keep the fouling in the bore soft. This will also aid in easier loading.
To clean your gun.....you're on your own.
Just kidding. Use plain old water and dish soap, a proper size jag and patches. Make sure to clean out that drum and nipple and don't forget the small hole at the breech. To help get the water out after cleaning, some use the non chlorinated brake cleaner and spray it into the breech, drum and nipple. Don't forget to oil the bore after. That brake cleaner will remove all oily residue and flash rusting starts almost as soon as the brake cleaner evaporates. To lube the bore, some use good old gun oil, some use Crisco or tallow, some use Ballistol and still others will use stuff like WD-40. Whatever works for you. Good luck.