This Instructable is an introduction to the basics of mold making for people interested in mold making with little to no knowledge on the subject.
It will walk you through some important vocabulary, break down the major mold types and help you select the correct mold for your project.
Here are some great mold making resources:
There are a variety of mold types for different applications:
Diagrams of the cross section of several mold types
Here is more information on Mold types.