First of all, IV's are set the moment you're egg is recieved or your pokemon is cought. IV's are a number from 0-31 attached to your six stats (HP,ATT,DEF,SP ATT,SP DEF,SPEED) and will determine your final stats at lvl 100. Lets say you get a pokemon to lvl 100 with a base stat of 215. If said pokemon has a max stat of 230, then you can calculate your IV as 15. Then that pokemon would have a lowest value of 199 and a highest value of 230. (Mind you this is assuming this stat is uneffected by natures). Natures take effect on the IV level, when stats are calculated game wise, the effected stat will be raised x1.1 or lowered x .9 depending on what your nature is. In the case of wild encounters, IV's are random, but you CAN breed for IV's using the day care. In the day care, a maxamum of three IV's may be passed to the offspring, but there are conditions. Firstly, both father and mother must have same IV in said stat, and secondly even if they do, theres always a possability of it not passing on. The remaining stats are generated randomly. So IV breeding is essentially breeding lots of pokemon and matching them up in the breeding center to achieve certian IV sets. It can take weeks to do it or you might luck out. Unfortunatly your IV's will always remain constant, there is no way to increase or decrease them.
EV's are diferent. Any new pokemon, newly hatched or just caught will have 0 EV's. As with IV's, EV's are values set to your stats. But unlike IV's, EV's add to your final stats rather then determine them. Every 4 EV points gained in a stat will ultametly raise that stat by one point at lvl 100. You can get a maximum of 510 EV points per pokemon. That includes all EV's from every stat, and a maximum of 255 in one stat (BUT only put a maximum of 252, or you will waste 6 EV's that won't add to your stats since 252 is the highest number divisable by 4). SO you can max out HP and att by putting 252 EV's in each stat, you will have 6 EV's left, which you can use to up another stat by one. You recieve EV points from beating pokemon, either wild or trained (but not from wi-fi/union room battles). Each pokemon has a certian EV value that determines what EV's it gives. For example, Charmanders will always give you one SP ATT, while Gyrados will always give you two SPEED EV's. There are certian ways to make EV training faster. Pokerus, macho brace and Power items, with power items being the best specialized items for use.
There are also beerys that lower your EV's. Have you seen any of the berrys that say "Increases freindlyness but lowers HP/ATT?etc"? Those berrys do not technichly lower your stats, but they remove the EV's you have accumalated in said stat. 10 points a pop, with the first berry taking you down to 100 if you have over 100 points in said stat. Also, as a note, vitamins increase your stats by adding EV's. But you can only use vitamins if your EV count is lower then 100 on said stat. Even if you raise that stat past 100 without Vitamins, it will have no effect.
I hope this helped, if you need more specific information as to where to find pokemon of specific EV's, theres a post in the previuos furom that points out a few good ones.