Archery units are proficient in non-magic ranged skills. Relatively weak defensively, but they excel in speed, which allow them to move and attack earlier than some others within a turn. With all things considered, it's recommended to put archery units in the back line, where they can move around freely and attack without having to face the opponents up close.
Primarily known as specialists in ranged skills, it's still possible for archery units to learn melee skills at low level, with Slash being one of Cavalry Archer's initial skills for an example. Archer and Cavalry Archer are listed as "Archer" and "Cav A.", respectively. Note that initial skills are marked with bold.