1) Your first step will be to go here (http://www.thingiverse.com/thing:277171), download the CAD files, and 3D print them.
2) Once you've got all your 3D prints and materials on hand, you're ready to pour your molds. The terms can get a bit confusing here, since all of the parts you just printed are called molds, and the silicone parts that you get out of them are also called… molds. It's molds all the way down. However, it'll make sense once you see what they're all for.
3) Coat the insides of your 3D printed molds in wax. This will help the final part pop out of the mold easily, in addition to sealing up any little cracks that would allow liquid silicone to pour straight through the print.
4) Fill all the molds to the top with Smooth-Sil according to the manufacturer's directions. Just pour in a thin, even stream starting the pour at the lowest point of the mold, allowing the wave of liquid that rises up to push any bubbles out. Once the molds are all poured, wait about 8 hours to de-mold.