Some people in Britain have a fairly small 'do' or reception after the wedding to which close friends and family are invited.
Then they have an evening (or night) 'do', to which many more people are invited.
Traditionally the bride's father paid for the cost of the wedding and the reception. Today, many couples expect to pay for at least part of it themselves. The guests do not expect to pay for their food and drink at the reception.
The evening celebration may well be held in a place with a bar. Guest will expect to pay for at least some of the drinks themselves, though the bride and groom may provide free drinks up to a certain amount/time. Depending on the venue, food may or may not be provided/available.
Some people, of course, still have a large reception with dozens or even, for the super-rich, hundreds of guests. Such people would not know the meaning of the expression 'evening/night do'.