Stand to sort out letters (7)
I believe the answer is:
'stand' is the definition.
(stand which supports something else)
'sort out letters' is the wordplay.
'sort out' indicates anagramming the letters.
'letters' is an anagram of 'TRESTLE'.
'to' acts as a link.
(Other definitions for trestle that I've seen before include "Table support frame", "Letters (anag) - table", "support for board", "Support for table top", "Supporting framework for, eg, table top".)