It seems that anyone with an existing Amazon account is already registered and just needs to sign in.
The main source format for the "self publishing" is HTML. You set the retail price and Amazon will pay you 35% of that price for each sold. (They reserve the right to sell for less than the retail price.)
They do seem to have a thing about you owning the copyright for the material that you publish and it seems that they will reject any public domain offerings from the self published arena.