How to heal others

In order to heal other players you will need a heal spell (not a "self" power). If you had taken at least a magician pack 2 during the character creation, you should have one, else, you will need to learn one from the magic trainer.
You need to target the player you wish to heal and click on the healing spell icon in the Hands Bar.
If the action does not appear in your hands bar, drop it from your progression window. or create it by right clicking on a free slot of the hands bar. Note that if you only have a 'self' power, you will not be able to heal other players.