I will use tart on cooking show (10)
I believe the answer is:
'show' is the definition.
(I know this)
'i will use tart on cooking' is the wordplay.
'i will' becomes 'I'll' (abbreviation).
'on' is a charade indicator (letters next to each other).
'cooking' indicates anagramming the letters (cook can mean to falsify or distort).
'use' after 'tart' is 'tartuse'.
'tartuse' with letters rearranged gives 'ustrate'.
(Other definitions for illustrate that I've seen before include "Show" , "Explain with pictures" , "picture" , "Ornament" , "Provide with pictures" .)