TC caplock percussion guns use #11 percussion caps.
The rifle can be loaded with 2F or 3F black powder or equivalent black powder substitute such as Pyrodex RS (rifle/shotgun - 2F) or Pyrodex P (Pistol - 3F), or Hodgdon 777. Note to use 15% less powder by volume if loading with 777. Do not load it with the pellet form of propellants, use loose powder only.
Projectiles that can be loaded are first and foremost patched round balls. The standard ball size to use is a .490 with a lubed .015 patch.
Bore size .50 caliber conicals can also be fired but be aware that they are sometimes harder to load and using a starter and sometimes even a mallet can be helpful.
.50 saboted bullets can also be fired but the barrel may frequently need to be swabbed between each shot or loading becomes very difficult and accuracy suffers.
There's many accessories to buy and details to learn about the cleaning and safe operation of a muzzle loader. They mainly need to be thoroughly cleaned after each shooting session. And one needs to be prepared and know how to handle any problem that arises.
Here's a PDF copy of the TC sidelock owner's manual which should be read thoroughly before firing it.
Is your friend available to teach you how to use it? I suggest to ask your friend to show you how to load it, fire it and clean if he knows how to do it.
Did it come with any accessories? Ammo and accessories that cost $50 - $75 or more may need to be purchased to be able to load, fire and clean it.
Are you sure that the barrel is in good shooting condition and that the gun is not currently loaded with powder and projectile?