How do I wire up a 4-wire dimmer switch when I only have two 2 wires from the wall?

Not sure what make and model dimmer you're trying to install, so I'll describe a common installation. Wire colors could vary, depending on manufacturer.

• Black is the common terminal, and is attached to the ungrounded (hot) conductor feeding the switch.
• Red is the switched lead (or a traveler in a 3-way installation), and is attached to the switched hot going to the light.
• Red with white is a traveler, used for 3-way installations. In your situation, you'll just cap this one off.
• Green is ground, and is attached to the grounding conductor.

^{From Lutron Luméa® Installation Guide}

If you don't have grounding conductors in your home, you could install a GFCI breaker and you'll be code compliant.

_{Lutron devices typically have a red and a red/white stripped wire, whereas Leviton has two red wires.}

Dimmer Switch for Alexa from Amazon. This is how I wired it to the existing 3 wires. The ground and neutral from the switch, green and white, had to be connected to the plain ground wire from the wall. The black wire from the switch, power in, had to be connected to the white from the wall. The white one from the wall could have been a black one when you have two black ones, in which case it wo u8 led be the one coming from the fuse box carrying 120v. The red one from the switch transfers electrical power to the lamp.