Welcome to Gaia! ::

IVs are Individual Values that each Pokemon is automatically already pre-programmed to have in it's Atk, Sp.Atk, Def, Sp Def, Spd, and HP stats. The highest it can be in any one stat is 31.

It is extremely rare to find a Pokemon that has a 31 in one of it's IVs let alone 31 in ALL of them.

Now how these stats affect Pokemon is like this.

Say you have a Garchomp and your friend has a Garchomp. Say your IVs are the same in every stat except for speed. Like this:

HP: 5
Atk: 23
Sp. Atk: 14
Def: 7
Sp. Def: 12
Spd: 30

HP: 5
Atk: 23
Sp. Atk: 14
Def: 7
Sp. Def: 12
Spd: 31

Let's also assume they both have a Nature that benefits their speed so that it may be as high as it can possibly go once you're done EVing and leveling up to 100.

Now say the both of you decide to EV train you Gachomps and place all the EVs in their speed.

The base stat is already 102 and you pump a ton of EVs into that and so the final product ends up with around 229-333 Spd.

You think that your Garchomp will be equally as good as your friends since you both EV trained the same way and both share the same nature but that's not the case at all.

Because your Garchomp has 30 IVs in speed and your friend has 31 in their's your friend's Garchomp will ultimately be faster than yours.

It works the same way with every other stat, Atk, Sp. Atk, Def, etc. Knowing your Pokemons IVs, having the right nature, and of course the right moves and strategy can mean a win or a loss in a battle.

There is some complicated way to find out what your Pokemon's IVs actually are, although it's not 100% accurate.

Serebii.net has a calculator here that you can use to figure out your Pokemon's IVs.

http://www.serebii.net/games/iv-calcdp.shtml

Also, it's very important to know your Pokemon's IVs in order to get it to have the right Hidden Power type that you want.

Yup no prob. It took me a while to figure it out too but once you get it, it all makes a lot of sense.