Depends on your OS. For Chrome on macOS, it'll show a chrome-styled square box with an icon and a piece of text in the upper right hand corner, kinda like macOS notifications (but they look nothing like it). In general, web notifications (can) work the same way they do on your smart phone. They can arrive from an active tab as well as from a background service.

Safari (on macOS) will use the native macOS notification system to display notifications AFAIR. I have no idea what IE on Windows does.

> I have no idea wat IE on Windows does.

https://blogs.windows.com/msedgedev/2016/05/16/web-notificat...

But in either case the browser has to be running I’m assuming? Seems kinda flawed.

JS service workers allow a JavaScript thread to run in the background while the browser chrome (the window) is closed. So, in theory, the browser doesn't need to be open. Also, notifications can be useful with an open browser too (or, multiple tabs with a tab in the background for example)

That depends on the browser implementation. The protocol does not require the user to have the site open.

On ChromeOS & on Windows with the Edge browser it integrates with the OS notification system. Not sure what Firefox does.