Gets on to the stage (6)
I believe the answer is:
boards
I believe this clue is a double definition.
'gets on' is the first definition.
('board' can be a synonym of 'get on')
'the stage' is the second definition.
(an actor 'treads the boards')
'to' acts as a link.
(Other definitions for boards that I've seen before include "Long flat pieces of wood" , "panels" , "Tread them in the theatre" , "Actors are said to tread them" , "Puts up" .)