They think about number one rock song site, releasing number (7)
I believe the answer is:
egoists
'they think about number one' is the definition.
The definition suggests an adverb but the answer is not.
'rock song site releasing number' is the wordplay.
'rock' is an anagram indicator (the solver must 'rock' the letters around).
'releasing' is a deletion indicator.
'number' becomes 'n' (n can represent any number).
'song'+'site'='songsite'
'songsite' with 'n' taken away is 'sogsite'.
'sogsite' anagrammed gives 'EGOISTS'.
Can you help me to learn more?
(Another definition for egoists that I've seen is " Selfish, vain types".)