4th Gen EV Training help?

Hey everyone, I hope this is in the right section...
Anyway, I was wondering if anybody would like to fill me in on EV training.
I have been out of the loop for a while, and I'm still stuck in Pokemon Red and Blue mode where stats didn't really matter...
I just ordered Platinum online, and I'd like to create a really good team. I'm trying to learn everything before it comes, that way I can start training right from the start.
So with that said, can somebody explain how it works?

I googled it, and got the basic information, but there are a few little details in which I need clearing up, such as:

How do I know how many EV points I have in a Pokemon?

Can I mix EV points? Example, can I get +4 in Speed, then +7 in Defense in the same level up? Or is it limited to one stat per level up.

Do you have to get all 4 EV points in order? Like, if I want +2 in Defense, do I have to kill 8 (for example) Geodude in a row, or can I kill 2 Geodude, then a Pokemon that gives 1 point in speed, then 6 Geodude; will any of the points cancel out?

I'm sorry if it's confusing. I'm trying to be as detailed as possible, that way I won't mess up my dream-team.

Thanks!

-There is no way to know how many Effort Values a Pokemon has without keeping track, although there are berries to reduce EVs that help with approximating.

-EVs can be collected in any order, at any level, regardless of whether or not any EVs were also added to another stat. They do not cancel each other out until that Pokemon reaches its limit.

There's a lady in Sunnyshore City that'll give your pokemon a ribbon if it's maxed out all its EVs.

More than one stat can be raised through EVs during a level up.

As far as I know, no, they will not cancel out or anything of the sort.

Please keep all questions regarding EV training to either our Q&A thread or Strategies & Movesets' Q&A thread.

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