Arts supporter's facility on line (5)
I believe the answer is:
easel
'arts supporter's' is the definition.
'easel' can be an answer for 'supporter's'. I am not sure about the 'arts' bit.
'facility on line' is the wordplay.
'facility' becomes 'ease' (I've seen this before).
'on' is a charade indicator (letters next to each other) (in a down clue, letters appear on others).
'line' becomes 'l' (used when specifying particular lines from a poem).
'ease'+'l'='EASEL'
Can you help me to learn more?
(Other definitions for easel that I've seen before include "Stand in a studio" , "Van Gogh's stand?" , "art supporter" , "Support in the studio" , "supporter of board, perhaps" .)