Flow is a trigger-based system for creating automated workflows. It allows your computer to automatically complete menial tasks which may be reducing personal efficiency. 

Plans 1 and 2 are the upgrade from Microsoft Flow Free. The main benefits of the more complete plans, are more workflows can be "run" per month, as well as the frequency of "checks" being increased. Checks are when Microsoft Flow uses it's connectors with other services, to check whether one of your workflows have been triggered. Plan 1 and 2 also have premium connectors which aren't available on the free version. Plan 2 exceeds Plan 1 in respect to organization policy settings, and business process flows.

The various plans which contain Microsoft Flow Plans 1 and 2, can be found in the image below.

The Microsoft feature comes with may of Microsoft Office 365 products available to you. For a list of the plans that offer Microsoft flow, click the direct link below

Office 365 Plan Options