The most widely available powder is Pyrodex and you will most likely use RS for rifles this powder is very corrosive so be sure to clean after shooting. The most commonly available bullets that are easy to get reasonable accuracy with are Shock Waves the 250 or 300 grain are good to start with. Dish soap and very hot water to clean with. I use Win 209 because they are the longest and so seal better against blowback.
I would recommend starting with 100 grains and if it does not group well the start going 10 grain increments in both directions.
Be sure you have a jag and patches to clean with and it is best to have a bushing that seats on the muzzle to protect your barrel.
Check your laws for hunting with a muzzleloader before you buy some states have weird laws like not using a scope or not using a sabot if you run in to this try the FPB 350 or 300 grain as they do not need a sabot.
Good shooting and if you have problem some one here will probably be able to help.