An Operation is counted every time a Flow successfully moves data or takes action for you. For example, if your Flow has an action to create new Google Contacts, each contact that is created will use one Operation.
The number of Operations you need depends on the number of active Flows you have and how frequently those Flows will run to automate your workflow. Don’t worry, if you use up all your Flows in a given month we’ll hold your Flows until you upgrade or your monthly usage resets.