Roger is upset about American - he complains (7)
I believe the answer is:
grouser
'he complains' is the definition.
The definition suggests a singular noun which matches the answer.
'roger is upset about american' is the wordplay.
'is upset' indicates an anagram (I've seen 'are upset' mean this).
'about' means one lot of letters goes inside another.
'american' becomes 'us' (abbreviation for United States).
'roger' anagrammed gives 'groer'.
'groer' placed around 'us' is 'GROUSER'.
Can you help me to learn more?
(Other definitions for grouser that I've seen before include "one to complain" , "One who has beef" , "Constant grumbler" .)