The button simply changed the details of the record to a static option.
For example, Set the Name field to say "John".
Or
Set the Statis field to "Active"
Here's some screenshots from my interface of what the set up looks like


Let me know if this helps
It looks like you're in a newer interface page with the new settings panel.
This is in the older 'blank page' layout and I don't have any other settings besides what's in the screenshot. I have no sub-settings to "Set" a field.
I figured it out. I didn't have a record selected, so it wasn't displaying the available sub-settings.