evs are an amount of stat gain you get when you level up. they are determined by what pokemon you killed. if you kill (for example) a zubat, you wil get +1/4 speed. you obviously wil need 4 zubats to get +1 speed. in this way, you can control what stats are increased the most. if you fought 8 zubats, you would get +2 speed once you level up. if you fought no pokemon during a level, you still get the set amount of stat gains as always. you only get 255(i think) evs to distribute to your stats. i know im missing something, but i forget what it is
ivs are the magic number that could make 2 (for example) adamant slakoths the same level have slightly different stats. i dont know much of ivs as you can see
if you want___, battle ____s
hp: whismur
atk: shuppet/poocheyena/trapinch
def: aron
spatk: spinda
spdef: tentacuel
speed: zigzagoon/zubat
those are the easiest IMO