Ports are spaces on the Game Board world map that are indicated by an island with a banner giving the name of the Port. Port spaces do not count as sea spaces, and player's can't make attacks from Port spaces, nor can they be attacked when their ship is in a Port space.
Players can Visit a Port as an action on their Turn if their ship is in a Port space. When you Visit a Port, Banish any enemies that you may have On Deck.
If a Port is covered by a Storm, it no longer counts as a Port until the Storm moves away; thus, the Visit a Port action is not available there, and ships on that space can be attacked.
Note: the game also uses the word "Port" as the nautical term for "left".
Directions
The game uses the nautical terms Port (left), Starboard (right), Bow (front) and Stern (back) to refer to different sides of the ship. This especially matters in regard to Artillery; both because Artillery Upgrades are installed in one of three slots (Port, Bow/Stern and Starboard), and because there are four Artillery Nodes (Port, Bow, Stern, Starboard) in the On Deck area.
Relative to a ship miniature on the Game Board world map, Bow is the direction of the hex in front of the ship, Starboard the next two hexes clockwise around the ship, Stern the third hex clockwise (thus the opposite direction of the Bow), and Port is the fourth and fifth hex clockwise from the Bow hex.