Hi Sith,
well you have a lot of different possibilities depending on what you want to mold. Yes, the most molds are made with RTV Silicone (meaning silicone that cures at room temp).
Galane has a thread going regarding this topic, and I believe there is also a short HowTo.
http://www.therpf.com/f11/making-rtv-silicone-molds-139755/
Google will be your best friend for finding information on this,,,, there is literally a wealth of information out there. check that out, the Smooth-On web site (
Mold Making Videos and Photo Tutorials presented by Smooth-On, Inc ), they not only have a bunch of introductory videos that are useful for getting an understanding of the different techniques but they also make a very good product for molding and casting.
Tip from me, start out slow make a one-sided mold first, then try a double-sided till you get it down and then let your imagination sweep you away.
hope that helps,
Jason