You'll need 1 to 1 1/4" flints. Dixie Gun Works sells them as does many other sutlers. The powder grain used is 2F. The flint should be wrapped in leather such that the beveled edge will scrape along the frizzen (hammer, steel, battery - depending on whose terminology you want to use) prior to being clamped into the jaws of the cock. Traditionally, either leather or a small piece of lead was used to secure the flint but I've been warned not to use lead as it adds to the weight and this can cause a casted cock to bend. Tighten the top jaw down such that the flint/leather doesn't shift.
Loading. Put the gun on half cock and open the pan. Soldiers use paper cartridges (paper roll that is sealed on both ends. Click
HERE for info on making your own paper cartridges). The cartridge had a measured amount of powder and a large ball (plus 3 buckshots).
Be mindful of where the muzzle is pointed at all times while you are loading the gun. With that long barrel, it's too easy or tempting to look down it. Please don't!Taking the cartridge, the soldier bit off the paper that held the lead balls (don't do this and I'm just advising you of the historical method). This exposed the powder in the cartridge and the soldier poured some powder into the pan and closed the frizzen over it. The remainder of the powder is poured down the barrel. The balls were then spit into the barrel and the paper could be wadded up and stuff down it to hold the balls in place. The ramrod was removed and used to push everything down to seat it against the chamber. The gun was then brought up and cocked fully back. On the command of present, the gun was shouldered and lowered (not aimed) towards the foe.
If paper cartridges are too much hassle, you don't really need them. All you need is a powder horn or flask, a measuring device and a bag to hold your lead balls.
Suggest you go to a National Park Site and ask a ranger. You can also try to find a reenactment group and someone there will be happy to show you how to use your musket. Then again, they'll try to show you the drill with the musket and make you wear a red coat or a hunting frock.