Flow permits individuals to automate business processes by building workflows based upon specific triggers and actions. An example of this would be a new item was added to a SharePoint list. A flow could be created that would trigger an email being sent to specific individuals requesting they review the item.
Flows uses graphical interfaces that permits an individual to easily and quickly design a basic workflow. This workflow can interact with other applications such as OneDrive, SharePoint and external applications. These flows can be created by opening the Flow App from App launcher or from any custom list or modern document library within SharePoint or OneDrive.
For additional information concerning Flow and how to create a flow select the appropriate link below:
What is Flow? - general information about flow
Getting started - information for individuals who have limited, if any, experience working with flows
Create a flow from within OneDrive or SharePoint - information on how to create a flow from within a custom list within a OneDrive or SharePoint site