@ Kavii
1: You leveled it up in-game? By battling? It's got EVs on it unless you solely used Rare Candies. You'll have to remove those EVs using EV-reducing berries (can't remember them off the top of my head atm but you can easily google them) before you EV train it. If you want to use it competitively...check its IVs and nature. If either or both are crap, you're better off getting a better pokemon. PS: IVs can't be checked using IV calculators unless you know your pokemon's EVs. Plug information into calculator and voila!, it spits out IVs. If you don't know your pokemon's EVs, remove the EVs. Furthermore, the closer your pokemon is to level 100, the more accurate the IV calculator. Many people look for IV battles because it sets your pokemon to level 100. All you have to do is scribble down its stats and punch it into the calculator.
2: Well, you get max 510 EVs and out of that, only 508 can be used (aka 2 EVs are wasted). Max 252 EVs in one stat and 4 EVs add 1 stat point to said stat. Those EVs gained add onto your pokemon's base stats (serebii.net has base stat info I believe). 127 extra stat points to place where you want them? Yum! As for IVs, I think how that works is the IVs of your pokemon gets added to its base stats. So you can breed an additional 0-31 IVs to your pokemon's base stats. This is assuming I'm remembering correctly.