It depends on what stats you want so here are a few pages to help you out:
The second page will also explain how to EV train plus there are many questions about how to on this Q & A. Just go look at questions under the "ev" tag:
Also for a location just use the second tab, find the Pokemon with the ev's you want to grind off of and find their locations. It's pretty simple.
Also, if you get it any ev's you don't want there are berries you can use to lower ev's, It just evolved though, so you don't need the berries, just thought I'd say it in case.
These guides WILL be helpful too, they taught me how to ev train:
This is pretty much the entire guide with everything you need to know!
Good Luck! IU know how annoying and hard ev training can be! :)
So Evs are basically hidden values for a stat. It depends on which stat you want. Go check locations.