It’s from the browser, on behalf of the website (for want of a better way to explain it).
If you say yes, it will alert you to certain things (I can’t remember what, because I have it disabled ) - new posts in your threads, somebody @mentioning you, those kind of things (I think).
You can change the setting in your browser preferences, so if you choose one option and then wish you hadn’t, it’s not irrevocable.
I might be missing something, but that link seems to be about handling notifications of the free upgrade to Windows 10 offer, rather than about notifications from this site on a Windows 10 system…
They’re transient so it took me a while to grab one. This is what they look like for me:
I have them allowed because I usually have a few tabs open.
If I’m viewing a page here, I don’t need to see the notification since Discourse does a great job at updating the notification indicator above my avatar.
But if I’m viewing a different site, the notification lets me know that “something just happened” here.
Notifications on Windows usually appear when something is needed or has been done such as updates or asking you to restart your PC. These notifications tend to appear at the far end of the taskbar. I don’t know where they are located on settings using top, bottom, and right. But since I normally use left, the notifications counter appears at my furthest bottom left corner. When you click on them, a side panel should appear expanding what the notifications are about. These notifications can also relate to emails if you sync your email with your Windows 10.