A double boiler, or a microwave to melt the soap in. A stirring utensil. Something to use as a mold. You'll probably want fragrances and scents, but it's up to you. There is some concern about using a microwave as you advance in soapcrafting.
Temperature control is one of the keys to making a good bar of soap.
For more on that, read on . . . The soap melts at about 140 degrees. If you want to use a thermometer, you can, however I never do. The key to MP soap is to not let it get too hot, not over 160 degrees. Soap which is too hot will burn, let off a bad odor, and loose transparency.