Call for help when discovered with a tin, rattled about for collection (6)
I believe the answer is:
entail
'call for' is the definition.
(entail can mean to call for or require)
'a tin rattled about for collection' is the wordplay.
'rattled' is an anagram indicator.
'about' indicates putting letters inside.
'for collection' becomes 'el' (I can't justify this - if you can you should give a lot more credence to this answer).
'a'+'tin'='atin'
'atin' anagrammed gives 'ntai'.
'ntai' placed into 'el' is 'ENTAIL'.
'help when discovered with' acts as a link.
This may not be right. Some or all of it may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for entail that I've seen before include "Inalienable estate" , "Late in (anag.)" , "legal restriction" , "settle estates for the long term" , "Restriction on inheritance" .)