The “Single Listing: Main Content” widget area controls the content on the on left hand column of a single listing. If you have changed the noun from “Listing” to another term this area will be called “Single {Noun}: Main Content”
By default the Description, Map + Contact, and Reviews widgets are loaded automatically. If you want to rearrange or remove any of these widgets then visit “Appearance > Widgets” and add a widget to the “Single Listing: Main Content” area. Please note, this will remove the other default widgets so you will need to add back any additional widgets you want to remain active.