Began to trade, perhaps, in beer (7,3)

'began' is the definition.
('start out' can be a synonym of 'begin')

'trade perhaps in beer' is the wordplay.
'perhaps' indicates anagramming the letters.
'in' means one lot of letters goes inside another.
'beer' becomes 'stout' (type of beer).
'trade' with letters rearranged gives 'arted'.
'arted' placed within 'stout' is 'STARTED OUT'.

'to' is the link.