I'm not sure what you mean by "how." Polymer clay can be baked in the oven (carefully) so you don't need a kiln. I just took polymer clay, sculpted it, baked it, and sprayed it with a waterproof seal. Then I drew on the red lines with marker and re-sealed it. My inspiration was Jupiter.
If you go to a craft store such as Jo-Ann's or Michaels you can find brands called Fimo and Sculpey in lots of colors. But even at Walmart you can often find the plain white kind. I use the plain white kind most often because it's cheaper to buy a large block of it. I sculpt all kinds of stuff so it's fine if the first few tries look weird--keep trying. After the clay is baked (but before it is sealed) you can also sculpt it to make it less rough-looking or to take away errant edges.
Another good trick to keeping it lightweight and helping it bake faster is to use aluminium foil as the "body" of the object then put the clay all over it.
