Basic concepts one's found in dirty books section (9)
I believe the answer is:
rudiments
'basic concepts' is the definition.
'rudiments' can be an answer for 'concepts' (rudiment is a kind of concept). I'm not sure about the 'basic' bit.
'one's found in dirty books section' is the wordplay.
'one's' becomes 'I'm' ('one is' is a formal way of saying 'I am').
'found in' is an insertion indicator.
'dirty' becomes 'rude' (I've seen this before).
'books' becomes 'NT' (New Testament).
'section' becomes 's' (legal abbreviation).
'im' going into 'rude' is 'rudime'.
'rudime'+'nt'+'s'='RUDIMENTS'
Can you help me to learn more?
(Other definitions for rudiments that I've seen before include "basic principles" , "Basics of any subject" .)