Hockey jerseys have existed for just over a century. Since their inception in the NHL in the 1910's, new designs for new teams and different designs from old teams have been made. There are so many different jerseys out there, particularly from the older years when designs were less standardized than they are today, leading to an abundance of opportunity for collectors.
A hockey jersey is a long sleeve sweater-like piece of clothing. It is used to show who the player is and what team he plays for. The colors on the jersey lets the fan know everything they need to know about each player.
Jerseys have changed greatly over the years. For example, many teams did not start out with putting jersey numbers on the back. Eventually this was done for fans to help distinguish players. Teams would use contrasting colors to help make the letters visible. Additionally, teams began using home and away jerseys to prevent color clashing with the opposing team.
With new events comes a new opportunity for teams to sell new jerseys. Companies such as Nike and Adidas have made many alternate jerseys for events such as the Olympics, with special logos as well. You can buy all of these jerseys at online stores for the team, league, and at the stores owned by companies that create the jerseys (currently Adidas but formerly Nike).