Havdallah is a Hebrew word from the root V-D-L, to separate.
The Havdallah "service" is a short service that is held at the end of Shabbat and Yom Tov (a festival) in Judaism). It marks the separation between the Holy and the Secular. The prayer is said (in an abridged form) in the Synagogue as part of the Evening Service at the termination of Shabbat, and also at home. It can't be recited until it is definitely night - traditionally when three stars are visible in the sky, although nowdays the times are pre-calculated in most Jewish communities and published in a calendar.
The exact components of Havdallah vary according to when it's being said.
- After Shabbat (including Shabbat and Yom Tov together)...
- An introductory paragraph
- The Bracha over wine - most Jewish services include this.
- The Bracha over spices. These sweet spices (often cloves are used) are to help the "sweetness" of the Shabbat carry over into the coming week.
- The Bracha over a flame. This is because on Shabbat we are not allowed to light a flame, so doing this now marks the separation. Traditionally a multi-wicked candle is used, or two candles held together. This gives a large, dancing flame.
- The Bracha "HaMavdil" - the separation. This Bracha talks about all the separations - "Between Holiness and Secular, Between Light and Darkness, Between Israel and the other Nations, Between the Seventh Day and the Six Days of Work".
- After Yom Tov (except when it's Shabbat as well)...
- The Bracha over wine.
- The Bracha "Hamavdil".
- The Bracha over the flame isn't made as we are allowed to cook on Yom Tov, and the Bracha over spices isn't made as Yom Tov doesn't have the same level of "sweetness" as Shabbat in the first place.
- After Yom Kippur...
- The Bracha over wine.
- The Bracha over the flame (as we're not allowed to cook on Yom Kippur).
- The Bracha "Hamavdil".
- After Shabbat, when it's still Yom Tov (eg Yom Tov is on Sunday), Havdallah is recited as part of the Kiddush for Yom Tov in the evening. The bracha over wine and "Hamavdil" are recited - however, the Hamavdil Bracha is modified to also talk about the differences between the holiness of Shabbat and of Yom Tov. The end of it, rather than "Blessed are you G-D who separates holy from secular" is changed to "... who separates holiness from holiness" to make it clear they are different levels.
Traditionally, the wine is poured into a becha on a plate, with some overflowing, and then the candle is put out in the wine after Havdallah. If wine isn't used, the "next best" is grape juice, followed by "the drink of the land". In England, the best candidates for this are tea or beer!