Book about many people in France (7)
I believe the answer is:
bretons
'people in france' is the definition.
(French ethnic group)
'book about many' is the wordplay.
I cannot really see how this works, but
'book' could be 'b' (abbreviation for book) and 'b' is found in the answer.
'about' could be 're' ('re' means regarding or about) and 're' is found in the answer.
'many' could be 'tons' (I've seen this in other clues) and 'tons' is present in the answer.
This accounts for all the letters.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for bretons that I've seen before include "Frenchmen" , "Natives of Brittany" , "Natives of St Malo" .)