In breeding, only IVs are passed down. EVs do not contribute to breeding in any way, positively or negatively. Natures can also be passed down, which multiply the final stat by 1.1 or 0.9 depending on what nature the Pokemon has. For competitive breeding, you don't necessarily need a ditto with 6IVs. I've bred many 6IV Pokemon with just 5IV dittos, but 6IV dittos definitely help. Either way, getting a 6IV Pokemon is based on luck and you're likely to hatch a box or two of eggs before getting what you want.
You can learn more about breeding here. For this particular question, scroll down to the section "Passing down IV stats."
You can find a list of natures here.
If you want to know more about EVs, you can read this article, but it doesn't serve any purpose in breeding, so reading this isn't as important as the other two.
