Stop walking across a dark room to turn on the light. Install a 3-way switch and control lights from two locations.

One way to think about it is that your far-end switch has two input lines (the travelers) and one output line (the common), which returns to the fan or light fixture.

The simplest setup is to have just two three-way switches control one light. A three-way switch has three screws on it, plus the green grounding screw.