Is available in tins, perhaps, if you demand (6)
I believe the answer is:
insist
'you demand' is the definition.
'insist' can be an answer for 'demand' (to insist on something is to demand it). I'm not certain of the 'you' bit.
'is available in tins perhaps' is the wordplay.
'available in' indicates putting letters inside.
'perhaps' is an anagram indicator.
'tins' with letters rearranged gives 'inst'.
'is' placed into 'inst' is 'INSIST'.
'if' is the link.
Can you help me to learn more?
(Other definitions for insist that I've seen before include "Demand forcefully" , "Urge" , "Be adamant" , "Maintain strongly" , "Press" .)