They help one to see good girls (7)
I believe the answer is:
glasses
'they help' is the definition.
Although both the answer and definition are singular nouns, I can't see how they can define each other.
'one to see good girls' is the wordplay.
'one to see good' becomes 'g' (abbreviation).
'girls' becomes 'lasses' (lass can informally mean a girl).
'g'+'lasses'='GLASSES'
Can you help me to learn more?
(Other definitions for glasses that I've seen before include "Specs" , "are they full of alcohol?" , "Spectacles; tumblers" , "Small refracting telescopes" , "Help in making out" .)