Movement is not an action.
Navy Ship: Attacking Pirate Ship
Merchant Ship: Selling goods, Loading goods
Pirate Ship: Attacking a Merchant Ship (only when the Pirate Ship is empty), Burying a Treasure
As the previous post states, one action can be performed during your turn either before, during, or after movement.
To be clear, Selling and loading goods is the same one action for merchant ships. You cannot load without selling or sell without loading, and it only uses one action.