The bare minimum is: Turn on any light, in honor of the Sabbath, before the Sabbath starts. But [Chabad has a decent article outlining how to do it right.](http://chabad.org/87131)
However, that guide is _Chabad_-oriented, and not everyone has _Chabad_ customs. In particular:
* It indicates you should give charity before lighting candles. That's certainly worthwhile, but is nor mandatory and many people don't do it.
* It indicates that single girls light candles. That's also not mandatory (except for girls living independently of their parents).