Q: How do I quick target a party member?

A: When you add a party member, they are assigned a number in the order that they are added. This number corresponds to your quick target. If you want to cast a spell on a party member, you activate the spell and then press the corresponding number. If you, for example, have a heal spell on your quick bar in the first slot and you want to heal the player that is third in the party list you would press the number "1" ,and then the number "3", and then enter.

Original answer by GM Shivers.