The EVs of a Pokemon are also known as Effort Values. Effort Values determine how many points a stat will gain before it reaches lv. 100. EVs are gained every single time a Pokemon gains experience. Each Pokemon gives a set number of EVs in one or two of the 6 stats of HP, Attack, Defense, Sp. Atk, Sp. Def, and/or speed. Unlike experience however, if more than one Pokemon participates in a battle, the EVs aren't divided. The amount of EVs and kind of EVs are determined by what Pokemon you're battling. A strong Pokemon like Machop, for example, will give 1 EV in attack. Its evolved form, Machamp, will give 3 EVs in attack. Important numbers to remember with EVs are that you can only have 255 EVs in a single stat and that you can only have 510 EVs total. Also keep in mind that for every 4 EVs in a stat, you'll gain 1 point in that stat. This also means that the ideal number maximum number of EVs in a single stat would be 252, since 255/4 = 63 with a remainder of 3. Since a stat boost is only gained when there are 4 EVs in a stat, having those 3 EVs would be a waste and could've been put in a different stat. This also means that you can only boost a stat 63 points from where it would be if it had no EVs at lv. 100. For example:
A Jigglypuff with no EVs in HP has 356 HP at lv. 100. If it has 28 EVs, that's 28/4 =7. Therefore, it would then have 363 at lv. 100 instead of 385. If it has 255 EVs, that's 255/4 = 63 R 3. Therefore, its HP stat at lv. 100 will be 419 (356 + 63). The same thing would happen with 252 EVs, since 252/4 = 63, except that those 3 extra EVs can go to a different stat since that would leave you with 258 EVs for use in other stats.
EV training is used to manipulate this gain of stats to increase the power of a Pokemon. Basically it's KOing the same types of Pokemon for maximum EV gain. Commonly used Pokemon are:
Bidoof in HP. (Route 201)
Machop in attack. (Route 207)
Geodude in defense. (Oreburgh Gate)
Gastly in sp. atk (Old Chateau)
Tentacool in sp. def (Surfing)
Zubat in speed (Ravaged Path)
Also, some people prefer to use Starly for speed instead (Route 201).
All of the above mentioned Pokemon give 1 EV in the stat specified. However, KOing 252 Pokemon is just as tedious as it sounds, so there are ways to speed up the process. The vitamins (Protein, HP, etc.) all give 10 EVs in the stat they say they boost. However, you can only use them 10 times for each stat. Since 10 x 10 = 100, you get 100 free EV if you give your Pokemon 10 of a vitamin. The Macho Brace doubles the amount of EVs you gain in battle. Pokerus, a very rare "virus" also doubles the amount of EVs you gained in battle. However, it is very difficult to obtain, yet very easy to spread to other Pokemon (if you don't have it yet, but would like it, use the trading forums and ask around). The last method of speeding up the EV training process is to use the "Power" items sold at the Battle Tower/Frontier. These come in 6 different varieties for the 6 stats and give 4 extra EVs to the stat they say they boost. For example, a Power Lens raises sp. atk. Battling a Bidoof while holding it would result in 1 HP EV and 4 sp. atk EVs. Battling a gastly with it would result in 5 EVs gained. In addition, the Pokerus can be used in conjunction with any of the other 2 battling methods, so you can have Macho Brace + Pokerus, or "Power" item + Pokerus. In my opinion, Pokerus + "Power" item is the fastest method. Battling a gastly with Pokerus and the Power Lens would result in 10 EVs gained sine (4 + 1) * 2 = 10.
IVs are also known as individual values. These are values determined at capture/obtaining and boost stats like EVs. Unlike EVs however, IVs can't be changed and range on a scale from 0-31 for each stat. Naturally, the higher the IV, the higher the stat will be. An example of application:
At lv. 100 with a 0 IV in HP, Jigglypuff has an HP stat of 340. If it had a 31 IV in HP instead, its stat would be 372 instead. Add this along with 252 EVs and you can have a Jigglypuff with 434 HP. A BIG difference from 340.
Did you understand this, do I need to explain more, or was it just tl;dr?
