Above all it's meant to keep you warm (8)
I believe the answer is:
overcoat
'meant to keep you warm' is the definition.
I can't tell whether this defines the answer.
'above all' is the wordplay.
'above' becomes 'over' (I've seen this in another clue).
'all' becomes 'coat' (I can't justify this - if you can you should give a lot more credence to this answer).
'over'+'coat'='OVERCOAT'
'it's' is the link.
Can you help me to learn more?
(Other definitions for overcoat that I've seen before include "Protective winter garment" , "Heavy outer garment" , "Evocator (anag.)" , "protective layer" , "Maybe Ulster" .)