What have we here but a torn sheet? (5)
I believe the answer is:
these
'what have we here' is the definition.
I know nothing about this answer so I can't judge whether it can be defined by this definition.
'a torn sheet?' is the wordplay.
'a torn' indicates anagramming the letters.
'sheet' is an anagram of 'THESE'.
'but' acts as a link.
Can you help me to learn more?
(Other definitions for these that I've seen before include "Sheet (anag) -- pronoun" , "The items indicated here" , "The persons or things here" , "Plural form of this" , "See 13" .)