The way you make your customized Pokemon game is easy: after loading the ROM into the program, start editing. You'll have dozens of things to change to create a unique experience.
The most noticeable change in Universal Pokemon Game Randomizer is your ability to choose the three first pokemon. From there, you'll be able to select where the wild pokemon appear, how they evolve, and their characteristics. You'll be able to create a truly original gaming experience.
Once you've created your Pokemon Pack, you'll be able to save and start playing the new game you've created. Keep in mind that you'll need the appropriate emulator in order to play.