Hard to have nothing in a carefully guarded store (5)
I believe the answer is:
hoard
'carefully guarded store' is the definition.
'hoard' can be an answer for 'store' (hoard is a kind of store). I am not certain of the 'carefully guarded' bit.
'hard to have nothing' is the wordplay.
'to have' indicates putting letters inside.
'nothing' becomes 'O' (looks like zero - 0).
'hard' placed around 'o' is 'HOARD'.
'in a' acts as a link.
Can you help me to learn more?
(Other definitions for hoard that I've seen before include "Secret stash" , "Accumulated store" , "Store, usually hidden" , "Amass secretly" , "Hard kick" .)