Its not really something that can be taught in type form. Much of it is technique outside of the monkey job basics. Smooth On has multiple videos and tutorials but you can also find other videos on youtube.
The question covers a lot of territory- what do you want to mold, what do you want to cast copies out of, what do the castings have to do? For example, if you're molding a glass bottle, you'd better be sure to coat it with a clear gloss, otherwise silicone will bond to it. Then, if you want to cast clear copies of the bottle, I'd recommend using a platinum silicone, as you don't have to bake it out for (some ) clear urethanes. Rubber (latex) mask making is a whole different animal, requiring stone (plaster) molds to absorb excess water/allow the latex to accumulate on the surface, and is water based, not silicone, needing acrylic/water based pigments, etc.