The Georgia Guidestones were built a few decades ago, paid for by an anonymous rich person. They used a pseudonym in their dealings with the contractors (I guess in the early 80's you could still do stuff like that) and nobody knows who it was. I don't think there's even any theories about an exact identity, but I could be wrong. To tell from the content on the stones it was probably some Elon Musk type, except emotionally mature and without the ego.
The stones were meant to be an instruction manual for rebuilding humanity in case some future natural or unnatural calamity wipes out most us and there's only a few million left. The same inscriptions are written in a bunch of different languages - including, for some reason, cuneiform and ancient Egyptian which is a weird pick? Like yeah, maybe one of the few hundred people living in the world who can read either of those fluently is gonna survive the apocalypse AND end up in Georgia but I'm pretty sure they'll also speak one of the actual living languages used on the Guidestones like English or Chinese.
But anyways, yeah it's mostly loopy feel-good stuff about living in harmony with nature, and some eugenics advocacy thrown in for good measure. It also talks about having a "world court", and that means every conservative thinks the Guidestones were put up by a satanic New World Order illuminati cult, hence that Kandiss Taylor tweet. They're on property owned by the county, so I guess in theory enough political pressure could get them removed.