Warmatrix

The first firearms like the handgonne and matchlock guns like the arquebus and musket were too large and unwieldy to be used from horseback. Nonetheless cavalry sometimes used "petronels", guns that were a compromise between pistols and carbines (short guns). The use of firearms by cavalry really took off with the invention of the wheellock in the mid 16th century CE. This allowed troops to carry guns into battle cocked and ready to fire with just one hand.
The first type of gun cavalry was the cuirassier. Cuirassiers developed out of men-at-arms, who in turn had developed out of Medieval knights. The two older types were characterized by the use heavy plate armor, horse barding and lances. Cuirassiers retained the body armor, but dispensed with horse armor and replaced the lances with small firearms like pistols, petronels or sometimes carbines.
Around the same time that cuirassiers developed, reiters appeared. They were medium cavalry: less well armored, but cheaper. Otherwise, they were similar to cuirassiers. They used pistols and swords, mainly against infantry, because they could seldom withstand a charge from enemy heavy cavalry. The Germans were pioneers in using reiters, employing them in deep formations.
The third category was light cavalry, who wore no armor at all except for maybe a helmet or a coat of leather. They wielded guns, swords and light lances. Examples of light cavalry were the Hungarian Hussars, not be confused with Polish winged hussars, who resembled lancers more; Stradiots from the Balkans; Spanish Jinetes; English border-horse. Light cavalry seldom fought in the thick of the battle, but did what light cavalry had always done: scouting, harassing, screening and pursuing.
A noteworthy tactic of gun cavalry was the "caracole" maneuver, in which they rode in a trot up to some 20 meters from the enemy, fired one or two shots and then turned back to reload and regroup. The effectiveness of the caracole has been questioned, but as the tactic remained use well into the 17th century CE, it must have been useful. Either with or without caracoles, the main method of attack by gun cavalry was to fire their guns at enemy infantry until they had been sufficiently weakened and then follow up with a more traditional charge, where they wielded their melee weapons.
In the 17th century CE the cuirassiers gradually discarded more and more of their bulky armor, until they were hard to distinguish from reiters. They were revived by Napoléon Bonaparte in the late 18th century CE.