A number of trees on the left provide shelter (4)
I believe the answer is:
tent
'shelter' is the definition.
(canvas shelter)
'a number of trees on the left' is the wordplay.
'a number of trees' becomes 'net' (I can't explain this - if you can you should believe this answer much more).
'on' is a charade indicator (letters next to each other).
'the' becomes 't' (the is pronounced as a 't' sound in some dialects).
'left' says the letters should be written backwards.
'net' after 't' is 'tnet'.
'tnet' written backwards gives 'TENT'.
'provide' is the link.
Can you help me to learn more?
(Other definitions for tent that I've seen before include "some guys held on to?" , "Collapsible shelter" , "Cloth shelter" , "Portable shelter for camper" , "Camping shelter" .)