Furnish with notes (3,2,5)

'furnish' is the definition.
Although both the answer and definition are verbs in their base form, I can't see how one could define the other.

'notes' is the wordplay.
I cannot really understand how this works, but
'notes' could be 'music' (musical notes) and 'music' is found within the answer.
The remaining letters 'setto' is a valid word which might be clued in a way I don't understand.
This explanation may well be incorrect...

'with' is the link.

Can you help me to learn more?