An action turn consists of 1 support action followed by 1 main action:
Gain and roll 1 dice of your choice from the dice pool.
Pay any resource to turn another dice to any of its sides.
Pay any resource to draw 2 cards.
...or use a support action on one of your unused blue cards. Then flip it sideways to mark it as used.
Play a card from hand, paying its cost.
Perform another support action as your main action.
Pay 3 heat resources to increase temperature 1 step.
Pay 3 water resources to place 1 ocean tile.
Pay 4 plant resources to place 1 forest tile (and increase oxygen 1 step).
Pay 3 city resources to place 1 city tile.
Pay 3 MegaCredit resources to immediately gain 2 VP.
...or use a main action on one of your unused blue cards. Then flip it sideways to mark it as used.
Free action: Some blue cards have free actions that may be taken at any time during your turn, before or after your support action or main action, or even at the start or end of a production turn. Perform the effect and flip the card sideways.
All your used blue action cards will be restored (flipped back) when you take a production turn.