Why is the Havdalah candle braided?

The bracha over fire is ideally made on a torch-like flame, so a Havdalah candle has more than one wick braided together to form a single, larger flame.

What are the requirements for a Havdalah candle?

It needs at least two wicks so it produces a torch-like flame. If you do not have one, two regular candles held together so their flames join can be used.

How do you use a Havdalah candle?

Light it before beginning Havdalah, make the bracha on the flame, and look toward the light. Afterward the candle is customarily extinguished in the leftover wine.