Why is a boats left side called port side?

Port is the nautical term (used on boats and ships) that refers to the left side of a ship, as perceived by a person on board the ship and facing towards the bow (the front of the vessel). The terms are also used for aircraft, spacecraft, and analogous vessels. The equivalent for the right-hand side is starboard.

An archaic version of the term is larboard. The term larboard, when shouted in the wind, was presumably too easy to confuse with starboard and so the Word port came to replace it,

referring to the side of the ship where cargo is loaded from the port.

The term larboard continued its use well into the 1850s by whalers, despite the term being long superseded by "port" in the merchant vessel service at the time. The term was not officially adopted by the Royal Navy until 1844

The term larboard was replaced with port because the term larboard could be confused with starboard but was replaced by port not because this is the side the cargo is loaded from but based on where the ship was headed. Back in the 1800s there was no way to correctly determine longitude. But latitude was very well understood. As long as you could see the north star you could determine what latitude you were at. This was done by measuring the angle between the north star and the horizon. Now if you are sailing out to sea you are most likely headed west because you would be leaving England and the north star would be on the right side of the ship or the starboard side. Once the ship turned north or south the ship sailed to the correct latitude of the destination then headed east along that latitude. At this point the navigator would be on the left side of the ship so the sails would not block his view of the north star. The crew knew if the north star was on the left side of the ship the ship was most likely headed east and therefore the ship was headed to it's destination to port. Thus the left side of the ship became know as the "port" side.
The anecdotal and perhaps apocryphal answer is thus:

Earlier vessels, most notably Viking longboats, were conned not with a stern rudder but with the rudder mounted aft and on the starboard side of the boat, as most people are right-handed. This meant that, when a boat tied up to a pier, it had to make fast along the side without the rudder, lest one accidentally damage the rudder.

Thus, the right side of the boat had the rudder or "steering board", which was shortened to starboard, and the left or port side was the side one exited the boat when visiting port.

Is it true? I don't think anyone knows for certain :}