Flow in a Flow is a way for you to bring a Flow that has only specific type of contents in it, inside another Flow. This is one way of putting company wide information and location specific information to the same Displays.
Most common use cases to use the Flow in a Flow Feature:
If you have a use case specific Flow, e.g. EHS Flow that needs to be seen in all Displays and a location specific Flow that is directed to a specific Display, you can put the more generic Flow inside the location specific Flow for easier management.
How to use the Flow in a Flow Feature:
First you need two Flows, one for a wider audience, and one for e.g. to be used in a specific location.
Choose the location specific Flow and click to open.
Then add the second Flow, set the weight and SAVE as you would with a Content App.
More detailed instructions can be found in the article Create a Flow - a fully automated content playlist