The means that an evening out on the town: a date, a party, a dance, a dinner, etc., initially was enjoyable. This sentence would be followed by a description of incidents that ruined what was initially an enjoyable evening.
It means that at the start of the evening, events were pleasant or encouraging or successful (and so forth). Usually, this is part of a contrast to what happens later.
The evening began well but soon things went sour. At nine o'clock, the clowns arrived with their squirt bottles and began to attack the guests.