Hey. I just tried replacing my light switch with a dimmer and came across a problem. The light switch uses two wires and the dimmer uses 3. The dimmer has 2 black and 1 green and the switch has 2 black. My question is, I know the black should be connected like in the switch, but where am I supposed to connect the green one?

There should be a bare copper wire in the box with the switch. Connect the green to that with a wire nut or compression lug.

The green wire is a ground. As Brian said should be connected to the ground wires in box( bare wires).

If no bare wires in box, connect to side of box, if metal, with a ground clip.

Chuck