Okay, first look at the gun and make sure it's marked ".45". Colt SAAs (Single Action Armies--that's what you've got there) and their clones have been made in LOTS of calibers besides .45.
If it is so marked, you'll need "bullets" marked ".45LC" or ".45 Long Colt". (Actually, they're called "cartridges"--the bullet is the lead tip that comes out of the barrel and makes holes in things.) You can buy them at any gun shop and at some big stores like Wal-Mart, or on the Web at these places and others:
Now, this is very important: make sure the gun isn't an old blackpowder one. There are ways to tell, but if you didn't buy it new, best to take it to a gunsmith and have him check it out. It's not safe to fire modern cartridges in old guns. Besides, some of thuse old guns are valuable collector's items and you wouldn't want to fire them anyway. Also, some very cheap copies of the Colt have been made, and some of those aren't safe to shoot at all.
Second, and this is even more important, do NOT load the cylinder with six rounds. Leave one chamber empty and make sure that one is under the hammer. With some exceptions, Colt-style single actions are unsafe when fully loaded; the firing pin on the hammer will be resting directly on the primer of the cartridge in the chamber, and a blow to the hammer will cause the gun to fire (for instance, if you drop it). Very dangerous.
Single-action sixguns probably aren't the best choice for beginners, anyway. If you haven't bought the gun yet, and you like the look of a single-action anyway, buy a Ruger; except for some old, rare ones, they're much safer than Colt-type guns.
Now about silencers: Bad idea. They're not hard to make, and books with plans for them are easy enough to find--but to be legal, they must be registered with the Federal government at considerable effort and high expense. Owning an unregistered silencer is a Federal felony and carries severe penalties--huge fines, prison, and like that.
If you want to silence the .45, forget about it anyway. Silencers don't work on revolvers. See that little gap between the cylinder and the barrel? That makes as big a bang as the hole at the end. Only autoloading pistols--the kind that don't have cylinders--can be silenced, as a general rule.
Best advice: join a gun club, take a couple of classes, and make some friends that can teach you about firearms BEFORE you buy a gun and start shooting. Gunners are, most of them, a friendly bunch and they love to share their knowledge. Before long, you'll know what you're doing--no offense, but right now you don't--and you'll know what you want and what you'll need, and you'll have a lot more confidence and be a LOT safer when you get started in shooting.
Good luck, and welcome!