Its both. You can tell from Pokemon you capture and ones you breed. Just look up an IV calculator on the internet and you can find out their IVs by typing in their stats. You won't be able to find out the IVs of your team Pokemon though because you haven't been keeping track of their EVs.
No it won't. It is better to learn about EVs before IVs. They are a lot less complicated.
Every Pokemon you KO gives you certain hidden values in the game called EVs. If you get 4 EVs in a stat, then that stat will increase by 1 extra when the Pokemon levels up. You can have a maximum of 252 EVs in one stat so that means EV training a Pokemon and giving him 252 EVs ina stat will ultimately increase his stat 63 points higher. That means like a un EV'd Pokemon would ahve 200 in a certain stat and an EV'd pokemon would have 263 in a stat. It really is effective in stat raising. You can give any Pokemon a maximum of 510 EVs total. So you can basically raise two of their stats by 63 points and then one of their stats by 1 point.
I have actually been trying so hard to understand it, but somehow it's just not sinking in... :'(
I know that beating certain Pokemon give you certain "points" in whatever stat they're highest in (starly = speed stat), and when you level up those points go to that stat and raise it.
I have no idea how to calculate IV's, though, and I think understanding that would help a lot in my understanding of EV's..