Came to a conclusion (5)
I believe the answer is:
ended
'came to a conclusion' is the definition.
(I've seen this in another clue)
'came to a conclusion' is the wordplay.
'came' becomes 'ed' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'to a' says to put letters next to each other (I've seen this in other clues).
'conclusion' becomes 'end' (something's conclusion is its end).
'ed' put after 'end' is 'ENDED'.
Can you help me to learn more?
(Other definitions for ended that I've seen before include "Broke off; finished" , "Concluded" , "Brought to a finish" , "Done" , "Stopped" .)