You choose a mirror you’ve seen on the same plane of existence as you. You create a scrying sensor inside that mirror. You can instead name an area, such as a specific building or city: you create a scrying sensor inside a random mirror within that area. If there is no mirror in the area, the spell fails.
You can see and hear from the mirror as if you were within it. If there is at least one creature within sight of the mirror when you cast the spell, you can take control of that creature’s reflection in the mirror. You can cause the reflection to act as you wish and to speak. Apart from the reflection’s appearance in the mirror and the words it speaks, it has no effect on the real world.