Hi mark, no expert here, but one would need to design a sprue of parts with vents, etc. and know about sprue and flow design for the material. Then you take your wax model and sucessively dip it in plaster until the wall thickness is good enough to pour. Most casters heat the mold prior to pour to remove the wax and so the material does not chill (harden) immediately when poured. After cooling the plaster is broken away hopefully leaving a complete part(s). some take the mold and put it into a spin-caster to use centrifugal force to push the material into the nooks and crannies of the mold in increase thae chances of having complete parts. Single parts can be done too, like one-off rings etc. I like the wall thickness reduction in the requirements for some finer casting.
