Hi Paige!
Mold-making is the process of creating a rubber mold from a clay original in order to cast duplicates in a permanent material, such as resin for example (see this video for further explanation: https://cgcookie.com/lesson/different-types-of-molds-explained/)
When you sculpt in polymer clay, however, this process is optional. A sculpture made of polymer clay can be hardened with heat (i.e. the oven) and thus becomes a permanent sculpture in itself.
If you still want to make copies of this hardened polymer sculpture you can, but it is not necessary as when you sculpt in oil-based or water based clay - both of which are NOT meant to create permanent sculptures, but merely the master sculpture to be molded and then cast in a permanent material.
So if you just want the sculpture for yourself and don't want to make a mold, polymer clay would be a good choice. After hardening this material can be sanded, primed, and painted.
I hope that helps! :)
~Lisa
