Tap , usually along the bottom of the screen, then swipe up, and tap 'Add to Home Screen'. More Info
Troubleshooting: if you don't see the 'Add to Home Screen' option, scroll to the bottom and tap 'Edit Actions', then tap 'Add' next to the 'Add to Home Screen'. After that, try again. Or see Apple's Guide
Note: With this version you get notifications while the app is open, but not when it is closed. Use the full app, instead for background notifications (if the Messaging installation supports this feature).
Tap the in the top right corner of the screen, and then choose 'Add to Home Screen'. More Details
Note: With this version you get visible notifications while the app is open, but only audible beeps when it is closed. Use the full app, instead for background notifications (if the Messaging installation supports this feature).
Click the or or style icon in the address bar, to the left of the address, and depending on the browser, drag this onto your desktop. More Details
In Edge on Windows, use > "Apps" > "Install this site as an app".
Why? You can run this app in a background tab within your desktop browser and get an audible beep when a new message arrives, from any of your subscribed forums. The tab should be highlighted, too.
, usually along the bottom of the screen, then swipe up, and tap 'Add to Home Screen'. 
in the top right corner of the screen, and then choose 'Add to Home Screen'. 
or 
or 
style icon in the address bar, to the left of the address, and depending on the browser, drag this onto your desktop. 
> "Apps" > "Install this site as an app".