I guess you know this far that i kinda suck at ev's and such XD

So anyway, now that i have more free time i decided to learn everything about competitive battles but there are still some things that confuse me.

I try to train most, if not all of my newly caught Pokemon according to ev's natures and such (i'm still trying to completely understand iv's) but as i said some things confuse me. If you want to raise a stat, let's say ATk for Tangrowth, you have to battle a Pokemon like Bibarel or Chatot. But in order to get the extra number in that stat you have to battle four of Pokemon who have Atk ev's? I don't get it. There are Pokemon like Bibarel who have 2 ev's.

When that is the case, do you only have to battle two Bibarel or the number doesn't count and it is still four?

Secondly, if your Pokemon has got the effort ribbon, if you try to reduce some unwanted ev's with the appropriate berry, would it work? And is there a way to find on what stat the ev's went, if you have messed up in training? I guess i know the answer on this... XD

Also, how do you know how to train your Pokemon according to stats, natures and such? I mean, how do you decide which stat to increase and what nature is right? I know there's always smogon and i've read a lot of pages over the past few days there, but i can't help but wonder why natures that increase the same stat as others are ignored. I have a Roserade with a Sassy nature and one of the smogon suggestions is a Calm nature Roserade. I get that speed is important but wouldn't ev training to increase that stat help? I just wouldn't mind not relying 100% on smogon and trying to make my own strategies.

Finally, and i do apologize if you're tired reading this, i was thinking of joining the smogon community in order to learn a few things right but since i'm already a member in a lot of forums i don't know if it would be worthy of my time.