Transparency in Yafray

I’m really sorry if this questoin has already been answered, but how do you make things transparent with Yafray on? Transparency works fine when I use Blender Internal, but when I swap to Yafray, it’s as if it switches off.

-Trexilence

I think it is controled by the alpha value in the color panel. I´m not using yafray much, but I think it´s that.