The closest I can come to describing sambar is to expect a cup of spicy lentil-vegetable soup; it's more like mulligatawny (or even hot-and-sour) than Campbells or Progresso though. Sambar and the coconut sauce are (usually) offered automatically with south Indian meals.
My other comment was a response to another poster's comment: "If you want to eat meat, why worry about authentic Indian food ...."
Here is a recommendation for you (depending on where you are located):
http://www.chowhound.com
There is a search feature there, along with a "hotposts" to see the most current listings if you haven't logged in there in a while.
One last point - you might think about trying an Indian buffet lunch first if your friend has never had Indian food before.