OK. EVs, where to start...

Every Pokemon gives out EVs. These EVs are known as an EV yeild. When we EV train our Pokemon, we keep track of those EVs (by counting them or writing them on a piece of paper like I do), therefore we know how many EVs te Pokrmon is receiving. When we reach the desired amount, eg. 128 EVs, we may move on to another stat and repeat the process. If you lose the numbers, you're technically screwed if you can't remèmber the number. In the Sinnoh games there is a 'counter' app that doesn't specifically say it shows EVs, but it will keep track of how many EVs your Pikemon has in one stat if you have received those EVs a few times in a row. If you receive a different EV, it will reset and begin on that stat. Other than that, there is no way to physically 'see' the amount of EVs; all must be done by counting and keeping track of numbers.

However, on PO and PS!, you don't need to EV train; simply entering the desired amount of EVs on that stat is all it takes.

Hope this is what you were asking!