EV's are Effort Values which are gained by battling pokemon that give out that specific EV. They are used to make Pokemon better in that stat. For example, Stoutland gives out 3 attack EVs. So if you want a Pokemon to gain some attack EVs battle some Stoutlands or other Pokemon that give out that EV. The EVs a Pokemon gives out can be found in their pokedex page on this site. You can also use stuff like Proteins,Carbos,Calcium etc to raise EV but you can only do it so many times. The best option is to battle the Pokemon because you can do this for however long you want. EV training is a very long process so you will have to be patient.