I really want a superflat seed with a ton of useful ores which are easy to find. How do I create a seed, and what programs do I use?
Seeds are not “created”, they are found by trying them. The seed is called that because it is the seed value for a pseudorandom number generator which is then used to determine all of the attributes of the world; it is computationally infeasible to design a seed to produce a desired result.
Type something for the seed, see if you like the world, and if not, try again with a different seed. Or look for seeds other people have tried; there are many web sites which claim to provide such information.