When you go to Rome, you do what romans do including how they speak. As a sailor, you have your own language hence the need to be familiar with the jargon used while at sea.
Aft - The back of a ship. If something is located aft, it is at the back of the sailboat. The aft is also known as the stern.
Bow - The front of the ship is called the bow. Knowing the location of the bow is important for defining two of the other most common sailing terms: port (left of the bow) and starboard (right of the bow).