Question

i mean do you need a special item ?or just train your Pokemon with a specific Pokemon
and how do you obtain them?

Answer 1

Just battle Pokemon with the correct EV. EVs are gained with Experience, so if you gain Experience, you are also gaining EVs.

Comments

but about how much ev does the stat level up?

Answer 2

On this website, go on to Advanced and click on Effort Values (EVs)
This will give you a very good description about EVs.

http://pokemondb.net/ev