What's that you said about Foot's bulk? (4)
I believe the answer is:
heft
'bulk?' is the definition.
(I've seen this in another clue)
'what's that you said about foot's' is the wordplay.
'what's that you said' becomes 'eh' (I am not sure about this - if you are sure you should believe this answer much more).
'about' shows that the letters should be reversed in order.
'foot' becomes 'ft' (abbreviation).
'eh' written backwards gives 'he'.
'he'+'ft'='HEFT'
Can you help me to learn more?
(Other definitions for heft that I've seen before include "Try to determine weight by lifting" , "Lift, carry; influence" , "Lift in order to heave, say an axe" , "Lift (something heavy)" , "Judge the weight" .)