
Explanation:

Box 1: Step
Each step represents a field where data can be entered.
Stages tell you where you are in the process, while steps are action items that lead to a desired outcome.
Box 2: Branching condition
You can enhance a business process flow with branching. If you have the create permissions on business process flows, you'll be able create business process flow with multiple branches by using the If-Else logic.
Box 3: Stage
Each stage contains a group of steps.
Reference:
https://docs.microsoft.com/en-us/power-automate/business-process-flows-overview
https://docs.microsoft.com/en-us/power-automate/enhance-business-process-flows-branching