Be in possession of a drawing and know what you'll do (4,1,4)

'what you'll do' is the definition.
I know nothing about this answer so I can't tell whether this works.

'be in possession of a drawing and know' is the wordplay.
'be in possession of' becomes 'a' (I can't justify this - if you can you should give a lot more credence to this answer).
'a drawing' becomes 'plan' (plan is a kind of drawing).
'and' is a charade indicator (letters next to each other) (I've seen this in other clues).
'know' becomes 'have' (synonyms).
'a'+'plan'='aplan'
'aplan' after 'have' is 'HAVE A PLAN'.

Can you help me to learn more?