Begins and principally wolfs one Chinese snack (4,8)
I believe the answer is:
open sandwich
'snack' is the definition.
(I know that open sandwich is a type of snack)
'begins and principally wolfs one chinese' is the wordplay.
'begins' becomes 'opens' (opening is a kind of beginning).
'principally' says to take the initial letters.
'wolfs one' becomes 'ndwi' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'chinese' becomes 'ch' (abbreviation).
The initial letter of 'and' is 'a'.
'opens'+'a'+'ndwi'+'ch'='OPEN SANDWICH'
Can you help me to learn more?
(Another definition for open sandwich that I've seen is " Something to eat".)