First you have to find a recipe. Then, when the moon is full and the stars are aligned...
No, actually, it's more simple than you might think--just make up a character mentally, give that character some abilities, a few hindrances, some personality traits, et cetera--basically, just put together a Person, and know exactly what they can and can't do. They don't even have to be human--they can be whatever you think up (but keep it within reason, Titans aren't likely to go over well).
See the thread about character posting for some examples.