To get the stuff, tear mail apart! (8)
I believe the answer is:
material
'to get the stuff' is the definition.
I can't judge whether this definition defines the answer.
'tear mail apart' is the wordplay.
'apart' indicates an anagram (the word is broken apart).
'tear'+'mail'='tearmail'
'tearmail' anagrammed gives 'MATERIAL'.
Can you help me to learn more?
(Other definitions for material that I've seen before include "Preoccupied with physical, rather than spiritual, substance" , "Fabric or other substance" , "grave" , "Directly relevant to a matter, in a law case perhaps" , "I alert ma (anag.)" .)