1. In Safari, open the web page you want to use as a web app.
2. From the menu bar, choose File > Add to Dock. Or click the Share button in the Safari toolbar, then choose Add to Dock.
3. Type the name you want to use for the web app, then click Add. The web app will be saved to the Applications folder of your home folder, and you can open it from the Dock, Launchpad or Spotlight.

https://support.apple.com/en-gb/104996