Indicates that D and E come before F and G, say (7)

'indicates that d and e come' is the definition.
'denotes' can be an answer for 'indicates' (I've seen this in another clue). I'm not sure about the rest of the definition.

'f and g say' is the wordplay.
I cannot really understand how this works, but
'say' could be 'note' (noting is a kind of saying) and 'note' is found within the answer.
The remaining letters 'des' is a valid word which might be clued in a way I don't see.
This may be the basis of the clue (or it may be nonsense).

'before' acts as a link.

Can you help me to learn more?