Skate guards are hard pieces of plastic that snap on to the blade of the skate. This is so the player can walk off of the ice without having to take the skates entirely off. The piece of plastic ensures that the blades do not get worn down on concrete, hardwood, etc. Not only are they preserving the blade, they are also preserving the floor surface that the player walks on.
Skate guards should also be on when the skates are in hockey bags. This ensures that the skates do not puncture the bag or cause any injury to the hand when someone reaches into the bag. Guards can be bought online or in any sporting goods store. They come in many different colors, and can even be designed with lettering and logos of the player's team and jersey number.