The end of something is its final point or farthest edge. After your cat unwinds a ball of yarn, you may find one end of it in your kitchen and the other end upstairs in the bathroom.
A piece of string has two ends, while stories, races, and years have just one end each. When you buy a length of fabric, the leftover bit is an end, and the final point of almost anything — a play or a marriage — is also an end. When you end something, you make it conclude. In football, an "end zone" is the far side of the field, and a "defensive end" is a player near the sideline.