On a three-way, there’s an extra terminal, known as the “common.” Power comes in for the switch around the popular, then two “traveler” wires hook up the 1st switch to the 2nd within the brass terminals. HomeTips posts may include inbound links to Amazon.com as well as other companion programs https://alexisihdzt.tinyblogging.com/fascination-about-wiring-to-lights-78486111