In Alchemy Stars, characters have different combat classes. These four classes are Converter, Detonator, Sniper, and Support. Classes will play into how you configure your team formations.
Converter[]
Converters are characters with an Active Skill that change tile colour, enabling your team to traverse the grid and (hopefully) connect more tiles.
There are three common types of converters: converters that change the colour of a number of tiles, cross converters which will convert all tiles in a cross shape from where their Active Skill is used, or tile resetters who reset the colour of tiles on the Alchemy Board.
Some of these characters also have additional Combat Mechanics that make them more useful in battle.
Detonator[]
Detonators are characters with higher damage-dealing capabilities, especially from their Active Skill or Chain Combo. For that reason, you will likely want at least one on your team at all times.
Some of these characters also have additional Combat Mechanics that make them more useful in battle.
Sniper[]
Snipers are characters that enable them to attack enemies from a distance, usually through both their Active Skill or Chain Combo.
Some of these characters also have additional Combat Mechanics that make them more useful in battle.
Supporter[]
Support characters vary in ability. They can Heal, provide buffs to your team such as Double Chain, or inflict a number of debuffs on Enemies such as Paralysis, Slow, or more.
Some of these characters also have additional Combat Mechanics that make them more useful in battle.