Read up on how to do breeding for Natures and IVs, and how to EV train. It's probably best to start with EV training, then once you've done a few Pokémon with that, breed some natures, and once you're used to that, learn to IV breed.
Once you at least know what they all do, play about on Pokémon Showdown. Probably playing Random Battles (which gives you a team) will give you an idea of what sort of strategies different Pokémon, then you can move onto playing in regular metagames where you choose your own Pokémon.
Nuggetbridge has a lot of good beginner articles, although a couple of them are mostly applicable to VGC, the official metagame, which is doubles.
Start here if you want to play on cartridge:
http://nuggetbridge.com/beginners/joeys-wisdom-natures-ivs-and-evs-for-newcomers/Or just go to Pokémon Showdown, click play, choose random battle, and off you go.
