Diablo 3 -
Kill him, and talk to the Templar. He'll offer to join your party if you so wish to have him accompany you. There's no negatives to accepting his help. If you decide to have him follow you, you can press F to see his equipment and spells he can use. Each follower has four tiers of spells they can use, each unlocked by your current level. In each unlocked tier, click one of the two spells to have your follower use that ability in battle.