Jewish holidays begin and end at sundown. that's because in Genisis it says "it was evening and it was morning: the first day." the holiday began last night at sundown. it's a two-day holiday, so it ends tomorrow evening. like the Sabbath, no work is to be done on the major holidays.
of course, not everyone observes all the rules. some are very strict in their observance, some not observant at all. I'm somewhere in the middle.