There arn't Pokeblocks in SS/HG. They are in Ruby, Emerald, and Sapphire. In those games, you go to the concert hall and go up to a pokeblock machine and work with other people there. You put a berry into the machine and use timing to try to make the machine go faster. How fast you get the machine and the type of berry you and the other people use effects how the pokeblock comes out (quality and type of stat (beauty, strength, cute, smart, cool) it effects). They also can be used to lure out Pokemon at the Saffari Zone. They have flavors that may make your Pokemon like or dislike you based on their preference.
In Diamond, Pearl and (I believe) Platinum, there arn't Pokeblocks, but Poffins that can be made in Hearthome city. They are essentialy the same thing, except you spin the batter and can work alone. These also are not in SS+HG
So, If you want a Milotic in SS (which I assume from the related question), you're going to have to trade for it. Having a Feebas won't help you, becuse you can't evolve it unless you trade it to a Diamond, Pearl, or Platinum game, evolve it, and trade it back.