With a three-way switch, you won’t be able to dim the lights at both locations unless you buy an expensive model (about $75) that has some souped-up circuitry.

Dimmers for a 3-way circuit have an additional wire. It includes a green ground wire, a hot wire, and two traveler wires, which are usually differentiated by distinct colors or by having one with ...

If you're adding a 3-way setup to an existing situation, this cable should be present already. Run a 14-3 NM-B cable (white, black, red, bare copper) from your first switch to the second switch.