As with scents, your additive will effect the final appearance of the bar in terms of clarity and color. You can use many things for molds. Cookie cutters, candy molds, Tupperware, yogurt containers, PVC pipe. Once you pour the soap into the mold, air bubbles will tend to rise to the top. Keep a spritzer bottle of rubbing alcohol or any clear alcohol and immediately spray the freshly poured soap.
Bubbles instantly disappear.
If you have any trouble releasing the soap from the mold, put the mold, soap and all, into the refridgerator, remove it in an hour and let it come up to room temp. Then pop the soap out. Let it dry 24 hours then wrap. Your soap is ready to use as soon as it hardens. If you want to sell your soap, you will have to wrap and label it.