A common way for audio engineers to route effects is via the track’s send output into a common FX return channel. This send-return relationship allows the mixer to share a single effect with multiple tracks, especially ideal for time-based effects like reverb and delay. Plus, it saves on DSP by using fewer plug-ins and sharing effects. Historically, when people wanted to add reverb or echo effects to their mix, they would generally do so by having some sort of echo chamber or a room where they would play a track out of a speaker and then record it at the other end with a microphone.
From the course Pro Tools 8: Mixing and Mastering, Brian White shows us how to use this send-return relationship in conjunction with FX in chapter 2, Working with the Pro Tools Mixer > Using sends and creating FX returns. This is a critical skill for Pro Tools users and Brian clearly explains how to master it, including how to best configure the effect plug-in, and how to listen to a preview to make sure the mix is what you want.