I want to install a dimmer switch in my bathroom. I have a 2 gang set up that controls 2 sets of lights. Each gang has 2 black wires and 1 copper wire. The dimmer switch that I want to install has 2 red wires, 1 green wire and 1 black wire. Which wires are supposed to connect with which? Does anyone have any idea how to install this? Thanks!

Generally, the electrical connections for the switch are either on the box or in the box for the switch.

Van you give us some more information regarding the model of the switch and the manufacturer of the switch, please.

Wiring on the switch you noted indicates it can be used for single or 3 way. Wiring diagram should be onbox. You will use 2 wires on single, all 3 on 3 way. HD has plenty, look at a switch there. Can't remember 3 way but for single pole, one red and 1 black.