How does DEI work exactly?

I know that DEI exists so everyone can have a fair shot at employment.

But how exactly does it work? Is it saying businesses have to have a certain amount of x people to not be seen as bigoted? Because that's bigoted itself and illegal

Is it saying businesses can't discriminate on who they hire? Don't we already have something like that?

I know what it is, but I need someone to explain how exactly it's implemented and give examples.