To exist as instructions in a nutshell (2,2,5)

'as instructions in a nutshell' is the definition.
I can't judge whether this defines the answer.

'to exist' is the wordplay.
I cannot quite see how this works, but
'to' is within the answer.
'exist' could be 'be' (synonyms) and 'be' is present in the answer.
The remaining letters 'brief' 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).

Can you help me to learn more?