So when you are ready to shoot, you want some .575 minie balls, and usually 2F black powder, or Pyrodex RS 2F powder substitute. You need a good muzzle loader powder measure, usually you will load around 60 - 70 gr for a minie, that or a little more for a patched round ball. Measuring powder is strictly by volume. You need a good ball starter if you are going to shoot round ball.
You also need some lube for the minie, I used Natural Lube 1000 from Thompson Center in plastic tubes. You can get regular scent (yellow) or pine in green tube, great stuff, also to protect the bore after cleaning, smells great.
The musket will also shoot round balls .570 diameter, using patches for .58 cal .010 or .015 thick, I recommend pre lubed T/C or other pre lubed type patches.
For cleaning, you want a rod for a .58 cal musket, cleaning patches (I think I used shotgun patches), a brass jag for .58 cal. For cleaning, nothing beats Black Solve concentrate, blue in plastic bottles. Makes 32 oz of cleaning in a std spray bottle you can get at Home Depot.
Last but not least, recommend you get a black powder reloading manual of some kind that covers muzzle loading rifle and musket basics.