In lay terms, when standing on the bridge of a ship (or any watercraft) looking toward the bow (front of the ship), starboard refers to the right side of the ship, port refers to the left side. At night, the port side of a vessel is indicated with a red navigation light and the starboard side with a green one.
The term starboard derives from the Old English steorbord, meaning the side on which the ship is steered. Before ships had rudders on their centrelines, they were steered with a steering oar at the stern of the ship on the right hand side of the ship, because more people are right-handed.Since the steering oar was on the right side of the boat, it would tie up at the wharf on the other side. Hence the left side was called port. The Oxford English Dictionary cites port in this usage since 1543.