Floor covered with rubbish and crumbs (5)

'crumbs' is the definition.
I know nothing about this answer so I can't judge whether it can be defined by this definition.

'floor covered with rubbish' is the wordplay.
'floor' becomes 'ko' (I've seen this in other clues).
'covered with' says to put letters next to each other (in a down clue, some letters go on top of others).
'rubbish' becomes 'pan' (both can mean to criticise heavily).
'ko' put after 'pan' is 'PANKO'.

'and' is the link.

Can you help me to learn more?