Extent of movement beginning to trouble composer (6)
I believe the answer is:
travel
'extent of movement' is the definition.
'travel' can be an answer for 'movement' (travel is a kind of movement). I am not certain of the 'extent of' bit.
'beginning to trouble composer' is the wordplay.
'beginning to' says to take the initial letters.
'composer' becomes 'ravel' (Maurice Ravel).
The first letter of 'trouble' is 't'.
't'+'ravel'='TRAVEL'
Can you help me to learn more?
(Other definitions for travel that I've seen before include "Go on a trip" , "Voyage" , "tour" , "Journey from one place to another" , "Make a journey" .)