title

ctrl+L
In there, create something you like, press create and you will open a page in your browser telling you the price. If you're ok with that, press create and it's created.

how do I see a preview?

you should see one on your tori while in the forger, you can see any edit to the flame you do immediately.
You might have flames turned off if you don't see it, type /opt particles 1 to turn them on.

ok also how does a different body part affect these flames?

The shape of a flame can be different, a head flame starts as a globe and a hand flame as a square. With most flames you can't really see the difference.
Other than that, it just changes the place the flame comes from.