A national airline carrying British pop group (4)
I believe the answer is:
abba
'pop group' is the definition.
(I've seen this before)
'a national airline carrying british' is the wordplay.
'national airline' becomes 'ba' (British Airways. I am not sure about the 'national' bit.).
'carrying' is a charade indicator (letters next to each other) (in a down clue, the bottom letters carry others).
'british' becomes 'b' (abbreviation e.g. in 'BBC').
'ba' after 'b' is 'bba'.
'a'+'bba'='ABBA'
Can you help me to learn more?
(Other definitions for abba that I've seen before include "Bishop" , "Form of address to deity" , "Eurovision prizewinning Swedish pop group" , "Waterloo singers" , "Father (NT)" .)