Looking happy - agreed about keeping money I left (6)
I believe the answer is:
smiley
'money i left' is the definition.
I can't tell whether this definition defines the answer.
'looking happy agreed about keeping' is the wordplay.
'looking happy' becomes 'mil' (I can't explain this - if you can you should believe this answer much more).
'agreed' becomes 'yes' ('agreed' can mean 'yes').
'about' shows that the letters should be reversed in order.
'keeping' means one lot of letters goes inside another (some letters kept inside).
'yes' back-to-front is 'sey'.
'mil' inserted inside 'sey' is 'SMILEY'.
Can you help me to learn more?
(Other definitions for smiley that I've seen before include "Grinning face symbol" , "Cheerful emoticon" , "Spymaster" , "sounds cheerful" .)