The new Shortcuts app, which is a reboot of the old Workflow app that launched with iOS 12, lets you create simple programs that use a variety of apps to accomplish a task. For example, the Time Machine shortcut for Photos lets you quickly pull up all of your photos from one year ago. This is just one of hundreds of pre-programmed Shortcuts found in the app's Gallery. To use a shortcut you need to first add it to your Library from the Gallery.
The Shortcuts app contains a gallery of many pre-defined programs that use one or more apps to achieve a desired result. For example, the Directions to Next Event shortcut uses the Maps and Calendar apps to quickly provide you with directions to your next calendar event. Aside from the shortcuts provided in the app, there are many avid users who share their creations online in communities such as Reddit and Sharecuts.
iOS 12's Shortcuts app has hundreds of useful shortcuts meant to make a variety of different tasks easier to accomplish on your iPhone. A reboot of the old Workflow app, Shortcuts has a gallery of pre-programmed 'recipes' that are basically small programs that use one or more apps to achieve a desired result. For example the Remind me at Home shortcut will remind you of a task as soon as you get home by using location services, Maps and Reminders. You could set this up yourself as a location based reminder, but the shortcut makes it considerably quicker and easier to do.
In iOS 12 Apple updated its Workflow app and changed its name to Shortcuts. A shortcut lets you quickly accomplish a task that would typically require a series of steps across a variety of apps. For example, the Home ETA shortcut uses the Maps app to find your distance from home and estimated time of arrival, then uses Messages to text your spouse/child/roommate/etc with a customized message letting them know when you'll be home.
There are tons of shortcuts available for the Shortcuts app, with new ones being created every day, and if you like to check them out then you have to add them to your library. This invariably leads to a cluttered library, so you'll want to get rid of the ones you don't use. Deleting shortcuts from the app's library is similar to deleting an app from your iPhone or iPad's Home Screen - just long press on it until all the shortcuts start to "wobble," then you just tap any shortcut that you want to remove so a blue check appears on it.