Something that’s served up route taken at sea? (4,6)
I believe the answer is:
main course
'something that's served up' is the definition.
(part of a meal)
'route taken at sea?' is the wordplay.
'route taken' becomes 'course' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'at' is a charade indicator (letters next to each other) (I've seen this in other clues).
'sea?' becomes 'main' (synonyms).
'course' after 'main' is 'MAIN-COURSE'.
Can you help me to learn more?
(Other definitions for main course that I've seen before include "big dish?" , "non-starter?" , "Marine biology, perhaps" , "substantial part of meal" , "sailors find trapping a lot of wind" .)