I can't even get it to too any of the ai stuff. It doesn't find faces or anything. I'm wondering if it could be my iCloud Photo Library. It's proven to be a problem in the past. Do we know if it uses the photos you have stored on iCloud or just the photos on your device?
As of beta 1, the UI is confusing. Faces appear in the albums section in the album called people, which is where other things like places also show up. As for how it works, your photos are never analyzed by Apple or sent to their servers (unless you use iCloud Photo Library or put the photos in a shared album, which obviously stores them in iCloud). All the AI Processing happens on your device wit the gpu (which is pretty cool if you think about it, though the abilities are limited by it not having the advantage of big data like a server based AI would). I used iCloud Photo Library too, and it took a few hours to process my 8GB library, but now it's all done and it does a pretty good job at categorizing photos. Not as good as google photos, but good for using an iPhone gpu.