Sort of skin, say, that is covering square (8)
I believe the answer is:
organise
'sort' is the definition.
(I know that sort can be written as organise)
'skin say that is covering square' is the wordplay.
'skin say' becomes 'organ' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'that is' becomes 'ie' (abbreviation for id est, 'that is' in Latin).
'covering' means one lot of letters goes inside another.
'square' becomes 's' (abbreviation).
'ie' placed around 's' is 'ise'.
'organ'+'ise'='ORGANISE'
'of' acts as a link.
Can you help me to learn more?
(Other definitions for organise that I've seen before include "Arrange in a systematic or orderly way" , "Catalogue" , "Devise and direct" , "Plan, direct, co-ordinate" , "Classify - Iron Ages (anag)" .)