Italian's land blunder occupies nice one (5)
I believe the answer is:
terra
'italian's land' is the definition.
'terra' can be an answer for 'land' (I've seen this in another clue). I am not sure about the 'italian's' bit.
'blunder occupies nice one' is the wordplay.
'blunder' becomes 'err' (to err is to make a mistake or blunder).
'occupies' is an insertion indicator (inserted letters occupy or enter the word).
'nice one' becomes 'ta' (both can mean 'thank you!').
'err' placed within 'ta' is 'TERRA'.
Can you help me to learn more?
(Other definitions for terra that I've seen before include "Legally land" , "Dry land" , "-- Firma; -- incognita" , "Centre" , "Latin word for earth" .)