On A 3-way, there’s an extra terminal, known as the “frequent.” Power comes in into the switch within the frequent, then two “traveler” wires link the 1st switch to the next over the brass terminals. DIYers must not, however, attempt jogging new wiring them selves—that’s a task for an electrician. https://louiskevkz.blogspothub.com/33861008/the-electric-hub-diaries