As important as they are to your safety, you've got to admit, wrist guards are a pretty strange looking piece of gear. It's no wonder people have a hard time figuring out how they're supposed to go on. (In today's beginner class, 3 out of 4 students started out with "Wrong way #1,"--shown below--before I checked their gear). Here's a little photo essay to make sure they protect you as designed.
Most wrist guards have a plastic splint on the top and the bottom to protect your wrist from injury when you use your hands to break a fall, which is an instinctive reaction that keeps your head from hitting the ground first. As with knee and elbow pads, the hard plastic makes sure you slide so that the sudden impact of a fall doesn't dislocate your shoulder. Wrist guards with plastic on just the palm side will still slide, but without spints both above and below the wrist joint, they don't protect against breaks or fractures. That's why I recommend full wrist guards for recreational and fitness skating, as shown in these photos.