how does encore/onstage/callback actually work (1 Viewer)

[killer queen]

all I know about these things is that you can get a nomination for performance/comp/choreo (or equivalent), what actually happens once you get nominated? do they pick the best out of the nominees? is there a step in between after nominations where nominated people have to like put their name forward for the final showcase?

anyways was curious, have a great night y'all