When does Shabbat begin and how do you know?

Shabbat begins approximately 18-40 minutes before sunset on Friday (the exact custom varies by community). The precise time changes each week and depends on geographic location. Candle-lighting times are published in Jewish calendars, synagogue bulletins, newspapers, and online (e.g., chabad.org). In Jerusalem, the custom is to light 40 minutes before sunset; in most other places, 18-22 minutes. Once the woman of the household lights candles and accepts Shabbat, all prohibitions take effect for her.