There are different explanations heard during my career in the navy.
Port side mean the left side when looking forward from the stern of the boat. Starboard means the right side when looking forward from the stern. Starboard is originally an anglo-saxon word literally meaning "right-side" or "right-board" and larboard is from the french baboard or the anglo-saxon bœc-bord. Anyway, there are discrepancies about what how port came from larboard, but basically it has stuck because larboard was too easily confused with starboard.
The another believe is, Centuries ago, what we now refer to as a rudder was lashed to the right side of the vessel. It was called a 'larboard.' When the vessel came into port, the captain didn't have much choice about which side to use since he could damage his steering gear if he had trouble. This must have led to term port side and larboard side..
Another interesting explanation is that Starboard was a walking board that hung off the right side of the boat. In the ancient days, navigators were depended on stars for navigational aid. The navigator of the ship used this Starboard to walk out where he could see the stars without the sails, masts and boat lights getting in the way. When the ship came in to Port, it could not port on the right side of the ship, or it would break the Starboard. So the left side of the ship was known as the Port side, and the right side was called the Starboard side.
Remember the lighting scheme of Port and Starboard? The Port light of an approaching vessel is RED; (Red Port wine). The red light tells you to give way to the other vessel. The Starboard light is GREEN which means you have right of way.
It is interesting to note that this practice carried over into aviation. Passengers almost always enter planes from the left, or port, side even though aircraft now have full sized doors on both sides
