One of the most basic (and frustrating) things to learn first on board a ship is port/starboard, aka left and right.
Basically, when the ship is moving forward and you look at it from behind, port is left and starboard is right.
However, you don't get off that easily, as it gets turned upside down when the ship reverses; now port and starboard are the left and right sides of the ship when viewed from the front. Therefore, the two "boards" will be assigned to the opposite sides of what they did before, when the ship was sailing forward. Yes, it's probably a sailor with too much rum on board who came up with this.
The terms originate from the Viking Age, when the heavy steering oar was placed on the right side of the ship because most Vikings were right-handed. So the right side became the starboard side, where 'board' meant wall.
The origin of the word 'port' is a little more controversial, but one obvious suggestion is that it comes from the Old Norse word 'bakka', which means a place to moor. Since the large, heavy steering oar was located on the right side of the ship, it was considered obvious to dock with the left side of the ship facing the harbor.