Ok, this is going to be a decently long post about tactical artillery use.

The first time that artillery can be said to have been decisive on the open battlefield in Europe is probably the Battle of Castillon, 1453, where French artillery devastated the English formations, including massed longbowmen.

There were two types of guns - cannons and mortars. Cannons fired in a flat arc and mortars at a high trajectory.

There were many types of ammunition and I'll describe what they were and what their effect were.

Solid round shot.

This could be stone (especially during the late medieval and renaissance era), led or iron. Iron proved to be the best option in the long run due to its toughness and ability to bounce. This was primarily used at a long range, and would be shot from a cannon at a low trajectory, and could by skilled artillerymen be made to bounce or skip over the ground, akin to how you can make a flat smooth stone skip several times if you spin it and throw it at a flat trajectory on water. These shots would bounce over the battlefield and tear anything in their way apart. This scene from the film 'The patriot' shows pretty well how a bouncing cannonball plows through the ranks of the Continental Army.

Since troops needed to manouvre and fight in close formations, both to make sure the commander could direct the troops and to not fal easy prey to enemy cavalry, a round shot plowing through a mass formation could kill or main scores of troops - and often severely traumatise those that were unhurt.

Grape shot

Usually consisting of 50-300 led or iron (most common lead) musketballs, each one about as large as a grape, thus the name, this kind of load was used to make the cannon a huge shotgun when enemy troops got close - usually about 50-100 meters. The usage of such a load could be absolutely devastating to closed and packed ranks of soldiers. Here's a video of a small 1pdr swivel gun firing grape shot. Imagine hoe devastating a 12pdr gun would be!

Case (or canister) shot

This is the same thing as the grape shot, but instead of loading loose bullets, the grape shot is packed in a thin metal case or wooden sabot which will crack or break after being fired (at different distances, depending on design and how much powder you use when firing it) and then spreading its musket balls. Basically, it is a grape shot that you can use at a longer distance that also adds shrapnel from the casing to the devastating. A video testing case shot with a US Civil War era gun.

Bombs (grenades).

These started out as very simple hollow round shots that were filled with gunpowder and had a fuse added. The fuse was lighted, the shot rammed down the cannon, and the cannon was fired. If the fuse was set correctly, the shot did not crack upon firing or landing, the greande would explode, ideally slightly above ground, and shower the troops below with red-hot shrapnel. A scene from the movie Glory, where the US navy is pouring grenades over Fort Wagner.

Now, artillery on the battlefield started out in earnest. Armies would bring siege artillery with them to deal with castles and fortifications in the late medieval and renaissance era. These would be big guns - heavy and demanding a large train of horses or oxen to move and usually more or less immobile once they had been deployed, as it could take hours or in some cases even days to move them. A gun could weigh up to 2 tons, not including the lavette and other equipment. Tactical artillery was mostly immoble on the battlefield.

Thus, artillery was usually deployed on a hill, ridgeline or other high point on the battlefield and used from there across the battlefield.

Guns of this era were either smithed iron or cast bronze, with the latter becoming more common as casting techniques improved - an invisible crack could mean that the gun blew up in the faces of the artillerymen and ignited gunpowder stores and became more dangerous to the using army than to the enemy.

While the Hussites and Cossacks were known to use small swivel guns mounted on carts to protect their camp and create an impromptu fortified and armed ring for the soldiers to fight out of in the 15th to 17th centuries, it was Sweden which first created the tactially mobile light artillery in the 1602s. First with the failed light leather cannon (leather and rope reinforcements over a thin iron or bronze barrel, which failed since the gun would overheat, since rope and leather did not let the heat escape as well as metal) and then with cast bronze 2 and 3pdr guns.

Sweden created these small regimental guns in addition to the traditional heavier guns to increase the firepower of the infantry. Individual guns would be placed between battalion and moved along with the infantry as it advanced and used directly against the enemy line. At Breitenfeld 1631 the Swedish forced used their light artillery not only to keep the Imperial Curassiers at bay but also to pound and devastate the massive Imperial Tercio infantry formations, while the Swedish cavarly actually captured the stationary Imperial cannons. The Swedish army made sure to train parts of the cavalry in handling guns, and for quite some time during the battle, the Imperial infantry was under fire not only from the Swedish artillery to their front, but also from their own artillery to their rear!

Sweden further developed the light artillery by adding the invesions of Carl Cronstedt. Anmarschbommar - rods that were fastened to the gun and allowed it to be pushed by infantry and artillerymen without limbering - and with the muzzle towards the enemy and geschwinda shots - pre-packaged gunpowder and solid shot that allowed the gens to fire at up to 10 times the rate of the muskets. At the Battle of Gadebusch 1712, the Swedish army moved its artillery through a swamp and arrived at the flank of the Danish army, allowing it to enfilade the Danish line while it wheeled - for more than an hour. Once the battle was joined by the infantry, the Danish army was ready to flee already.

The Prussians, who as Brandenburg had been allied to Sweden in several wars started to develop light horse artillery which could follow the cavalry at speed and give them some firepower and merged light and medium artillery in the 12pdr gun, which would more or less become standard in western warfare until the invention of the interrupted screw breech and the recoil system.

Napoleon would add artillery tacts of the grand battery, collecting dozens or hundreds of guns together in one unit that could quickly devastate any enemy unit trying to manouvre on the battlefield.

By this time, artillery had become enough of a concern that a defending side always tried to build earthworks to protect its troops against devastating artillery bombardements. These earthworks would during the Crimean War and US Civil War start to evolve into trenches which protected the troops better against both solid shot and grenades than earthworks did.

During the early 1800s, rifled cannons, which could fire further and more accurately started to make their appeance. Still the 12pdr Napoleon smoothbore bronze gun was the most common piece of artillery during the US Civil War. The Austrians came up short at the Battle of Solferino 1859 with their smoothbore artillery against the French rifled artillery, and had by the time of the Battle of Königgrätz 1866 switched to a uniform rifled artillery that outmatched the Prussian artillery.

By now cast iron techniques were good enough to create iron or even steel guns which could load heavier loads of gunpowder and were more resistant to heat (and thus needed less time to cool down). Many countries were experimenting with modern style grenades with time or impact fuses instead of burning fuses and breech loading. However, it was not until the French invented the interrupted screw breech and the modern recoil system that modern artillery as we know it appeared.

Artillery would now fire at alarming rates, out of sight of enemy troops by using forward observers and fire grenades spreading deadly shrapnel in all directions almost exclusively. They did not need to re-sihgt or re-aim the gun after firing a shot due to the recoil system. Getting the spent grenade out by simply opening the interrupted screw breech and loading a new one in a matter of seconds.