What is reverb
Reverbsimulates acoustic spaces. If you clap your hands in a bathroom or concert hall, the sound is quite different. This is due to the fact that in enclosed spaces reflections build up and overlap to create the reverberant sound. Reeverb parameters allow you to simulate different types of acoustic spaces. If you wish to give your acoustic and electronic instruments a realistic (live) feel, then use of reverb is critical.
There's more information in the video, watch it to know how to use it