This will tell you about EV's :http://pokemondb.net/ev
Basically EVs are Effort Values, which you get by defeating other Pokemon. For Every 4 EVs your pokemon obtains, there will be one point raise in that particular stat. However, it is important to note that they will not be added immediately, but will be added in the long run, by the time the pokemon is Level 100.
EV Training is a term used to specify the situation when a Pokemon defeats another Pokemon in battles, speciffically for the EVs.
Eg : Defeating Patrats for 1 EV in Attack, etc
Hope this helps :)