Exploit first appearance on river (9)
I believe the answer is:
adventure
'exploit first' is the definition.
'adventure' can be an answer for 'exploit' (I've seen this before). I'm not sure about the 'first' bit.
'appearance on river' is the wordplay.
'appearance' becomes 'advent' (Advent is an example).
'on' is a charade indicator (letters next to each other) (in a down clue, letters appear on others).
'river' becomes 'ure' (river in Yorkshire).
'advent'+'ure'='ADVENTURE'
Can you help me to learn more?
(Other definitions for adventure that I've seen before include "Exciting exploit" , "Risky or exciting experience" , "Risk" , "that may be exciting" , "The thrill" .)