So I've never played in groups before

[Aetheryal-sargeras (Aetheryal)]

@Epheria-pagle

There is a fairly standard use of raid marks (the large symbols you may sometimes see above a mob’s head).
Skull = primary target
X = secondary target
Moon = sheep, this is your target to polymorph
Square = hunter trap

There are other marks, but they get used less and are less standardized. Any tank using them should specify in chat what they are being used for.

This is invaluable information! Thank you so much.