This wristband has a working LED light sewn into the fabric. When you connect the metal clasps, the light turns on. When you open the metal clasps, the light turns off. This is similar to many circuits that you have created using various electronics kits, but uses metal thread sewn into fabric as the conducting wires.
Here is a rough sketch of the circuit. The gray lines show the metal thread that connects the parts of the circuit. The picture shows the thread as a line, but you can actually use any stitches you want to create an interesting pattern, as long as the stitches connect from one LED wire to one side of the battery, the other side of the battery to one part of the clasp, and the other part of the clasp back to the other LED connector wire. (Which sides? You'll want the positive side of the battery to flow to the positive side of the LED.... experiment or ask to find out which is which.