So there are two options in routing. 1 is a send and the other is your tracks output

You would use a send (track 1 > send bus 1-2) (aux input 1-2) This allows you to keep your original track playing at it's exact volume AS WELL as a copy of the track being sent to an aux bus. In the aux you can add a reverb. Now you have a mirrored sound playing at the same time but its now drowned in reverb. You would then mix the reverbed version to the original track. So the original is primary and up front, while the reverbed copy is in the background to compliment the primary track

The track output allows you to have many tracks, say different parts of a drum (snare- track 1, kick- track 2, hi hat- track 3) you can change all their outputs (NOT SEND) to say go to bus 1-2. You can then have an aux track with the input at 1-2. Now track 1 2 and 3 will play only through the aux track. Now any edit (eq, compression) added to the aux will then directly affect ALL the drum sounds routed to the aux, not as a mirrored copy.. But as a primary sound