Answer:
These are the cannons used during the Civil War. This is the field artillery of the time before it expanded.
What were cannons used for in the Civil War?
Various cannons were used but the two most used where the two main Field Guns, the 12 pounder Napoleon, named after Napoleon III who designed it in 1858 and adopted by both sides. It was smoothbore generally made out of Bronze, Bronze is both stronger and lighter then Iron in cannon designed for use in the field (Bronze was also more expensive then Iron).
The 12 pounder Napoleon was made throughout the war and was seen as the most effective cannon of the war. The US was still mostly forest in 1861, and the max range of the Napoleon of 1500 yards was more then adequate.
The other main cannnon was the Three Inch Rifle Cannon. The Three Inch had longer range, one gunner said he could hit a man at a mile, but a smaller shell. It had a very good reputation, only one blowing up in the Civil war (cannons blowing up had always been a problem with cannons). Very accurate, very powerful a good complement to the Napoleon.
The Three Inch was made of Iron but had a steel core in its chamber. I.e. steel was made first and the Iron poured around it to make a very strong cannon. Cannons barrels are made up of several bands of steel not the one piece of Iron or Bronze of Cannons before the 1880s. The Three Inch Rifle was one of the first example of using bands of metal instead of one solid piece of metal.
The Napoleon lasted till 1874 when it was ruled to be obsolete given the development of Cannons by the Germans in the Franco-Prussian war of 1871. The Three inch rifle served till after the war with Spain in 1898.
Smaller cannons were used, mostly “Horse cannons” light guns as light as “Four pounder” a cannon designed to shoot a four pound round shell. These guns were designed to be hauled on the backs of horses as opposed to be towed behind.
Remember a horse can carry 400 pounds on their backs, but 2000 pounds in a wagon. Horse Artillery were designed to be hauled in pieces with no one piece more then 400 pounds. Field cannons were designed to be hauled by 2 horses, thus, including the cassion to haul ammunition, about 4000 pounds. Please note Horse Artillery men rode horses, field cannoners walked with their cannon.
Now larger cannons were used, including mortars. Most were hauled by train to the area of the Siege then by oxen to they firing position. This could take as many as 20 oxen per gun. Oxen were used for they can haul more then a horse, eat worse graze and last longer but at slower speed. A horse hauling a max load will still go faster then a man's walk pace, but Oxen will go slower.
These large cannons were hard to use but could destroy things the field guns could barely dent. Most were made of Iron, for Iron was cheaper then Bronze but at the size of these guns the advantages of Bronze was just not worth the extra costs of Bronze. Most were melted down post war, or still on various forts built during the Civil War for it was decided it was not worth hauling them out of those forts. Many of these forts were in deep swamps hauled they to shoot at confederate forts, hauled to their firing position and then left there after the fort had fallen as not worth it to haul them out. These guns are still in those swamps.