Course starting with exam referring to what's on reef (5)
I believe the answer is:
coral
'reef' is the definition.
(coral reef is a kind of reef)
'course starting with exam' is the wordplay.
'starting' indicates taking the first letters.
'with' is a charade indicator (letters next to each other).
'exam' becomes 'oral' (spoken academic test).
The first letter of 'course' is 'c'.
'c'+'oral'='CORAL'
'referring to what's on' is the link.
This may not be right. Some or all of it may belong to another bit of the clue.
Can you help me to learn more?
(Other definitions for coral that I've seen before include "Main resident" , "Marine substance, often forms reefs" , "Pinkish-orange colour" , "Deep pink colour" , "Creature building reef" .)