Gave an account of fourth-rate brothel, terribly seedy for the most part externally (9)
I believe the answer is:
described
'gave an account of' is the definition.
(I've seen this in another clue)
'fourth-rate brothel terribly seedy for the most part externally' is the wordplay.
'fourth rate' becomes 'D' (fourth best category after A, B and C).
'brothel' becomes 'crib' (I can't explain this - if you can you should give a lot more credence to this answer).
'terribly' indicates anagramming the letters.
'for the most part' means to remove the last letter (most but not all of the letters).
'externally' indicates putting letters inside (some letters go on the outside of others).
'seedy' with its final letter removed is 'seed'.
'seed' is an anagram of 'esed'.
'crib' going into 'esed' is 'escribed'.
'd'+'escribed'='DESCRIBED'
Can you help me to learn more?
(Other definitions for described that I've seen before include "Represented in words" , "Reported" , "Portrayed in words" .)