https://dotesports.com/news/what-are-ivs-and-evs-in-pokemon
This might just be better, but I'm providing a tldr still
EVs: Effort Values (EVs) are stat point that a Pokémon gains by fainting another Pokémon. For example, if, say, your Gengar fainted a Magikarp, it will gain one Speed EV, and so on. What EV a Pokémon gives depends from species to species.
The total amount of EVs a Pokémon can have in their whole stats (HP, Atk, Def, SpA, SpD and Spe) is 510. You can divide these 510 in any way you wish to, but the maximum one stat can have is 252. Ergo, you'll see offensive breakers usually with 252 Atk/SpA and 252 Spe, to maximise their damage output and Speed.
Now, 4 EVs give one stat point at Level 100. Let's say you have a Pokémon X. Now, X's base stat of, say, Speed, at Level 100 is 100. Now if you train X with 252 Spe EVs, it will gain 252/4 = 64 more stat points, making the grand total of Speed to 100+64 = 164. The is the same with other stats also. For Defensive Pokémon, training them might be harder as you'll want to outspeeds some foes before they attack you and do anything, or maximise one Defense but do some of the other (Def or SpD) to take some hits in the respective category.
I guess that's all for a small tldr lol
IVs: IVs can't be gained y fainting wild Pokémon. They're already assigne to your Pokémon when you catch them. They can range from 1, the lowest, to 31, the highest. Like EVs, this also change the grand total of any stat at Level 100. Let's say you have a Pokémon Y. Y, at Level 100, will have a Speed stat of 100, without any EVs. Now, if its Speed IV is 1, its Speed becomes 101. If its 31, then the Speed stat becomes 131, and so on.
Usually you'll see 0 Atk on Pokémon which don't have any physical move to lower the damage from Foul Play and Confusion. 0 Spe is usually seen on Pokémon with Gyro Ball f any move like that or Pokémon on Trick Room teams. Suicide leads such as Slurpuff do 0 HP/ 0 Def/ 0 SpD so that they can trigger their item (Focus Sash) with any strong/medium-strong move for whatever reasons.
I guess that's all lol tbh tht link might be better, wall or Discord me for any other question related to Competitive Pokémon!!
And nice chain lol thanks