What would Sauron actually "do" with the One Ring?

Everybody is terrified that Sauron will get the One Ring and be unstoppable. But, what is he even going to do with it? Like... What does the One Ring do, other than make people turn invisible (which isn't even that useful because the ringwraiths will just come and kill you)? Or it allows control of the lesser rings of power, which isn't even useful because the Ringwraiths are already under Sauron's control, and the Dwarves have lost their rings or are dead. And the elves won't put their rings on. So the mind-control aspect of the One Ring seems pretty moot in actual practice.

I've seen people say that if Sauron gets the One Ring he'll "be restored to his full power" but what does that actually mean? Because Sauron isn't going to be able to shoot death beams or something. Isn't his skill/power in crafting? But he's already crafted his greatest work, the One Ring itself. So if he got restored to his full power, he could... craft some more rings that everybody now knows are trapped, and nobody will put on anyway? This does not seem that useful.

So what does the One Ring even do? If Gandalf actually took it for himself, how would he use it to overthrow Sauron? Or what would Galadriel even do with it? How would she become the terrorizing queen?