Get your selection > Save to channel > Set channel as selection
How do you use things like pen, paintbrush, fill, exc. at this point?
When I go to use them they are in my edit history but I don't see it making changes to the picture.
To use paint tools in the selection mask we may toggle to quickmask view (Select > Toggle Quickmask Shift + Q):
Now when using paint tools they are shown in the red quickmask layer:
On toggling back to normal view we can see the usual selection dotted lines: