An adherent and he understands what's going on (8)
I believe the answer is:
follower
This clue might be a double definition.
'an adherent' is the first definition.
(I've seen this before)
'he understands what's going on' is the second definition.
The answer is a person as well as being a singular noun. This is suggested by the definition.
'and' acts as a link.
Can you help me to learn more?
(Other definitions for follower that I've seen before include "Person who succeeds" , "One accepts the leadership of another" , "A devotee or a pursuer" , "Supporter" , "A loyal adherent - or a pursuer" .)