hello this guide explains about Iv's and how they work to help your pokemon get a upperhand in battles. A Iv is a individual value and can range from 0 to 31.
Ex: 2 magnezones, both are modest nature, level 100 and fully eved in special attack but the first one has 328 special attack and the second one has 359 your thinking howcome one magnezone has a hight amount in specal attack? The first magnezone had 0 ivs so it got the lowest amount of specal attack possible even though fully ev'd while the second magnezone had 31 ivs in specal attack so they were added on and it has the highest specal attack possible for magnezone.
Each of your 6 stats: Hp, Attack, Defense, Sp. attack, Sp. defense, and Speed has a Iv value 0-31. The way to determine your Iv's is by not eving your pokemon and have a Iv battle which gets them to level 100. Then you copy the number of the 6 stats and enter them in a Iv calculator (serebii and metalkid have one) and it tells you your pokemons Iv.
To get a good Iv pokemon without hacking or the use of action replay it is hard to but eggs have more higher ivs then wild pokemon do because they get their ivs from their parents. If the pokemon's parents have good iv's then the egg will also have good ivs because it takes some from its parents. When raising a pokemon make sure there ivs are averagely good enough so it isnt a waste of training at least above 15 so you get something out of it. Sometimes 1 status point is all that matters when going to KO a pokemon.