[Each Grail Front map has a set number of slots, each pertaining to a certain class. You can put your Servants in the corresponding slots and equip CEs to them up to the map's cost limit.
Once the game starts, you move your Servants and yourself along the map as much as your movement points per turn allow. If your Servant is next to an enemy Servant or Master, you can use movement points to attack them, which triggers a battle.
Battles are generally 1 vs. 1 with each party having a turn to act for each party member. If you have your Servant attack an enemy Servant with another enemy Servant next to them, it'll be a 1 vs. 2. If your Servant attacks while having an allied Servant next to them who's in position to attack, it'll be a 2 vs. 1.
ST Servants like Bond CE Herk are busted for this, but depending on the situation AOE Servants and supports can be equally valuable. It's a versatile game mode with plenty of options for fun.]