Go to the Latex Casting Guide and read up on how to mix resin. Put the silicone mold you've just made onto a level surface (outdoors) and pour the resin into it slowly. Blow on the resin gently to remove air bubbles.

Wait 24 hours. After the resin sets, peel the newly cast object away from the mold. (Again, this should be easy although you should keep the silicone from sticking to itself.)

Voila. You're done. The silicone should stand up to several castings. (Depending on what type and/or strength the silicone is. Most places that sell silicone will list this information for you.)

Now it's time to move onto--

Finishing and Painting...