Wait... wha??? What is EV training?
Serebii has a pretty detailed description of EVs and how to train them. It is outdated a bit now with the release of Sword and Shield, but still goes through the general gist of it:
Serebii.net Games - Effort Values
A couple of things I'm not sure he explains well. First, different Pokemon award different EVs types for defeating them, and different amounts. So you need to seek out those different Pokemon in order to boost whichever specific stat you're looking to increase, if you're going to use that method for gaining EVs. A typical physical attacking Pokemon will look to add 252 EVs into Attack and 252 into Speed, and the last 4 into one of the defenses or HP. A special attacking Pokemon typically 252 in Special Attack and 252 into speed. Defensive Pokemon often have a more complex EV setup. There are of course other EV spreads used for offensive Pokemon, but most examples do as I described. Smogon is a good resource for what EV spreads you can look for. I grabbed Aegislash as an example, to continue from the post you quoted:
https://www.smogon.com/dex/sm/pokemon/aegislash/
You no longer have to worry about going over 252 EVs like he is describing, as it is now capped at 252 and has been since I believe gen 6.
Sword and Shield made it so that there is no limit to the number of Carbos, Protein, Iron, etc that you can give to your Pokemon, so that is currently the easiest method of "training" EVs right now. But they are expensive. Another way to do it is at the job thing with the Rotom PC that is in the pokecenters. Otherwise you can do it by defeating specific Pokemon in the wild, but that seems like too much work anymore, especially since horde battles and SOS are no longer a thing.