The Relative Volume Adjustment edit panel is used to display and edit relative volume adjustment frames for the current file selection. The intent of these items is to allow you to specify how much you want to increase or decrease the volume of the track on various channels. There can be more than one Relative Volume Adjustment item in a file but each description field should be non-empty and unique.
All editing and manipulation is done via the context menu and is described here.
Yate does not, (at this time), provide a dedicated editor for Relative Volume Adjustment frames. It allows you to enter the hexadecimal characters (0-9, A-F, a-f), representing the frame's content. The layout of data in an Relative Volume Adjustment frame (RVA2) can be found in the ID3 specification available here: id3.org
It is extremely doubtful that you would ever have to use these items or that you would encounter them in files. They are included for completeness.