Howdy! I'll try to explain things in a way that hopefully will make the most sense. I'll generalize a bit too because color spaces are complex :)
The ACES OT operator in Corona takes care of the tone mapping part according to the ACES specs. To put it in layman terms, it'll tone map the image in that filmic ACES style and so the highlights will look more "natural" and the darker parts will get a nice treatment as well. You'll also notice that depending on the intensity of the colors and the exposure you're using that the colors will behave much more like they would if you were taking a photo with your camera. That's what the ACES OT operator does.
The ACES tone mapping part is just one bit of what ACES does as a whole though. Primarily it is used to offer a color space (or a set of) that artists in a production can easily transition in and out of. Without it it's harder to keep everyone on the same page because converting between all the different color spaces that are out there is... Tough. This whole ordeal is not implemented in Corona at the moment. From my understanding that would be the OCIO part mainly.
The ACES color space can also be used for rendering calculations. Some renderers use the somewhat color limited sRGB color space to calculate things under the hood. Other renderers, like Corona, use wider ones. There's pros and cons to each but generally speaking the current trend is that more is better and since ACES offers a really wide gamut of colors it is typically what gets implemented as the color space in which renderers make it calculations these days. As mentioned though, Corona always used a wider color space so it's pretty much ACES like from the start. Are there wider color spaces than ACES? Yep. But ACES is just kind of becoming the one everyone is getting used to working with lately plus its wide enough as is. TLDR though, Corona is using a wider color space by default and while it isn't exactly like ACES it's more similar to ACES than to sRGB. And again, from my understanding there's pros and cons to sRGB and wider stuff.
So the above is again, a bit generalized but hopefully it helps understand things a bit better :)
Oh and dully noted on the tutorial part. We're giving this one a +1. Thank you!