Okay perhaps I am dense, but the description of the atropal's actions includes: touch, ray of cold, life drain and summon wraith.   Can it do each of these each turn or only one of them? 

Simply put...

Anything listed as an Action is to be performed as a normal action, and I believe the Atropal only gets a single action per turn.

Anything listed as a Legendary Action can be performed between player turns (but not after the player before the Atropal's turn order).

These Legendary Actions are to allow "boss" monsters more actions/attacks to make up for basically being outnumbered.