EVs

Currently shiny hunting Charmander on Delta emulator but I’ve never quite understood EVs and wondering if someone can explain. How do they directly correlate to the base stats you see on your Pokémon (Attack, defense, speed etc.)? I am also wondering how much these base stats truly make a difference. I am ~7500 resets in and the lowest stat I’ve seen is an 8 and the highest is 14. Is it really that massive of a difference for the stat to be a 9 vs a 12 for example? Does giving a carbos/protein etc. essentially raise what the corresponding stats base number would be? A lot of questions, I know, but I would rather hear from someone directly who knows what they are talking about as opposed to searching online. Any help is much appreciated. Thank you!