Started composing ode with writer (6)
I believe the answer is:
opened
'started' is the definition.
(opening is a kind of starting)
'composing ode with writer' is the wordplay.
'composing' indicates an anagram.
'with' indicates putting letters inside.
'writer' becomes 'pen' (something which writes).
'ode' with letters rearranged gives 'oed'.
'oed' placed around 'pen' is 'OPENED'.
(Other definitions for opened that I've seen before include "Unlocked, made accessible" , "Turned the key, facilitated entry" , "Started, a meeting say" , "Undone, begun" , "unwrapped" .)