Breeding Questions?

[Lucario3D]

So im very new to competitive pokemon battling and im trying to build my first team, but I dont know how people get 5-6iv legendaries like landorus, heatran, zapdos, and others. I know how to EV and IV train as well as breed pokemon so I have all that down, the only part im confused about is getting 5-6 iv legendaries with a blue pentagon?

Thanks for the help!