https://www.theverge.com/2018/9/17/17847104/apple-siri-shortcuts-ios-12-app-download-features

Apple is making Siri a lot more powerful in both iOS 12 and watchOS 5. Siri’s new Shortcuts feature is now available to download for iOS 12 users, and it allows iPhone and Apple Watch users to use Siri to step through multistep routines. Shortcuts replaces the previous Workflow app that Apple acquired last year, and is designed to allow you to create custom commands in Siri that launch apps or combine a number of actions in a similar way to IFTTT.

You can do things like tell Siri you’re “watching a movie” and the digital assistant will switch your phone to do not disturb. A number of app developers are also launching their own custom Siri shortcuts with iOS 12, which will help the assistant display more information when you create a custom phrase. Citymapper is one of the first big apps with Siri shortcuts support, allowing you to create a shortcut to ask “when’s my next train” and get relevant updates and even platform information.