The heat's terrible and he goes inside to get under cover (7)
I believe the answer is:
sheathe
'cover' is the definition.
(to sheathe something is to cover it)
'the heat's terrible and he' is the wordplay.
'terrible' indicates anagramming the letters.
'and' means one lot of letters go next to another.
'heats' anagrammed gives 'sheat'.
'sheat'+'he'='SHEATHE'
'goes inside to get under' is the link.
I am not very happy about this link. Some or all of it may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for sheathe that I've seen before include "Put (a sword) into case" , "stow away safely" , "Cover in case" , "Put (a sword) it its cover" , "Put away (a sword)" .)