help needed with switch installation please!
A single pole switch has two screw terminals. A 3 way switch has 3 screw terminals of which two are usually brass and a third which is usually black. The two brass screw terminals are called travellers and the black screw terminal is called the common terminal.
I highly recommend the Black & Decker book "Basic Wiring & Electrical Repairs" which gives detailed instructions on how to wire 3 way switches.
Hope this information helps and good luck with the repair.
The switch you replaced probably had a direct connection to the hot wire. There should be an extra wire in the box that you did not connect. That would be a traveller wire to the other switch. The traveller wires connect the two three-way switches so that the hot wire can always be turned on or off from either switch. It is an ingenius system that should have been named after the guy who figured it out.
Get the book, and read up on 3-way switches so you can diagnose which wires are which and do it right.