Thanks for the feedback. Did you try to change the key bindings in the settings menu?
The spells have a tooltip description. The attack spell does damage overtime and you can see a debuff on the boss bar with the same icon.
Maybe I should change the color of the damage number when they come from the healer making it more obvious.
You also have 2 vfx associated to the cast of the attack and it landing on the boss.
I am not sure if you are familiar with mmo healing. It mainly works with mouse over.
So when you mouse over a target the heal will be launch on him at the end of the cast.
You can either mouse hover the bottom bars or the characters directly.
Which version did you play? Did you defeat all the bosses?