PokEdit - What the heck is PokEdit?
PokeGen - PokeSav FAQ
^ Two Pokemon editors and the FAQs for them. Different editors have different ways of working, but basically a Pokemon editor allows you to create perfect Pokemon instantly, i.e. ones completely to your choice, rather than having to breed & train them. You send these edited Pokemon into your game by essentially hacking your game.
Obviously, doing this is not recommended because hacking into your game will cause glitches, and you might end up losing all information on your game.