One generously putting a bit of money in the door? (5)
I believe the answer is:
donor
'one generously putting a bit' is the definition.
I can't tell whether this defines the answer.
'money in the door?' is the wordplay.
'money' becomes 'n' (I can't justify this - if you can you should give a lot more credence to this answer).
'in the' is an insertion indicator.
'n' inserted inside 'door' is 'DONOR'.
'of' is the link.
Can you help me to learn more?
(Other definitions for donor that I've seen before include "One giving to a cause" , "One who gives blood, for instance" , "Someone providing" , "Giver, of blood say" , "One who dishes out" .)