We use mirrors in so many ways in our lives. As well as using mirrors to check our own appearance, we can also use them to see what's going on around us.
Mirrors in cars keep us safe on the road by allowing us to see what's coming up behind us. Curved mirrors on sharp bends in the road let us see what's coming around the corner.
Multiple mirrors can be used to make periscopes, so that we can see from a different angle. For example a submarine uses a periscope to see the surface of the water.
The Infinity Box uses a one-way mirror, which is see-through on one side, and partially reflective on the other. If a one-way mirror is lit on one side, but not the other, you can see through the mirror from the dark side, but not from the lit side.
One-way mirrors are made from glass with a thin layer of metal. The metal used is usually aluminium. This metal gives a reflective surface, but lets some light through because of how thin it is.
These kinds of mirrors can be used in various kinds of tricks. Pepper's Ghosts are illusions created using one-way mirrors that are often used in Haunted House fairground rides. A "ghost" is put behind a one-way mirror. When the "ghost" is lit up, it is visible, when it is not, the mirror reflects back the rest of the room. This way, the "ghost" can be made to appear and disappear.