House has two black and one white. dimmer has one black, one green and one red. WHat connects to what? THanks

Black wires are the hot side the power line, white is the neutral, and green is ground. On your dimmer, the black wire is for the AC input and the red wire is the output to the lamp you want to control.

If you are replacing an old switch with the dimmer, the two black wires will be connected to the screw terminals on the switch. One of those black wires is the AC feed to the switch, the other black is the one that goes to the light fixture. You'll need to determine which is which so you can hook the dimmer up correctly.

For a few dollars you can pick up a tester that lights and chirps when it's near a hot wire. Turn off power to the light circuit at your circuit breaker or fuse panel. Remove the old switch and disconnect the wires. Make sure the bare ends are not touching anything and turn the power back on. Hold the tester near each of the black wires. One of them will cause the tester to light up and the other one will not. The unpowered wire is the one going to the light fixture. This one connects to the red wire on the new dimmer. The hot wire is the feed that connects to the dimmer black wire. The green wire on the dimmer connects to the other green wires already in the box. Turn the power off again and make your connections using UL approved twist-on connectors (wire nuts), which probably came with the dimmer. Fit the wires and dimmer back into the switch box, secure it with the mounting screws, replace the cover plate and turn the power back on.

Voila! You'll have a working dimmer. A Google search for "installing dimmers" will turn up several links to sites with good pictures.