Assuming you've sculpted a prototype out of sulphur free clay, and have created a silicone mold for it, this isn't terribly too hard to do.
I use SynAir products (there are many others as well) which include their liquid resin known as Por a Kast and their mold release ---SynLube 531.
You really don't need mold release for silicone molds, since nothing but silicone will stick to silicone, but you can spray a thin coat of the SynLube every so often into your mold. As for the resin, the Por a Kast commonly used is the Mark 1 or Mark II variants. I prefer Mark 1 because it cures faster (about 2 min.) and machines better. The Mark II cures to a bright white color, and is lighter in weight. For an excellent how-to on the molding/casting process go here: www.danperezstudios.com/workshop.htm