In this video we use the new JSON Function in PowerApps, to format a local collection in PowerApps before sending it to Flow. Once in Flow, we use the Parse JSON Action to extract the collection data, which opens a myriad of options that can then be formed using this data.
See below docs for the new JSON Function in PowerApps:
https://powerapps.microsoft.com/en-us/blog/json-for-canvas-apps/
For a quick introduction into JSON, see one minute into the below video:
https://youtu.be/E_WFwAZI7lU