Tees consumes gin, served up at one: clues initially incomprehensible (9)
I believe the answer is:
enigmatic
'incomprehensible' is the definition.
(similar in meaning)
'tees consumes gin served up at one clues initially' is the wordplay.
'tees' becomes 'me' (where the crossword setter is 'Tees').
'consumes' indicates putting letters inside.
'served up' says the letters should be written backwards (in a down clue, going upwards).
'one clues initially' becomes 'ic' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'me' enclosing 'gin' is 'mgine'.
'mgine' in reverse letter order is 'enigm'.
'enigm'+'at'+'ic'='ENIGMATIC'
Can you help me to learn more?
(Other definitions for enigmatic that I've seen before include "Like a puzzle" , "Mysterious or puzzling, like Mona Lisa's smile" , "not obvious" , "Mystifying" , "Ambiguous or puzzling" .)