Youll have to excuse how bad I am at explaining, but I'll try my best. Firstly, ignore EVs, they are irrelevant to breeding (although I can explain how they work if you'd like). The easiest thing to explain is natures.
Natures each have a 1 in 25 chance of being received. How can you make that more likely? Make one parent hold an everstone and their nature will always be passed down!
IVs, however, are much harder to explain. Firstly, I'll assume you know what I mean by a 'power item'?
To check your IVs, use an online calculator and/or talk to the guy in Kiloude City. You want him to say that all your stats can't be better (this is extremely unlikely, one or two is great, but if all 6 you don't need to breed).
Now, choose a male and a female with good IVs and breed them. 3 IVs will be passed down.
Example.
Male: 12/31/13/17/9/31
Female: 18/9/31/31/4/29
The ideal baby here would inherit 3 31's. The other three stats are randomly generated.
How can you ensure a stat is inherited? Well, this is where power items come in. They can be held by either parent to ensure a stat is passed down (Power Lens = SpA; Power Anklet = Speed etc.). THIS ONLY WORKS ON ONE PARENT.
And finally, the Destiny knot, if held by either parent, means 5 IVs will be passed, not 3, which is incredibly useful!
Did that clear everything up? Or is there something you don't get?