Beneath the tab settings you choose which of the earlier created publishing flows should be activated for the current page. You can choose to inherit, stop the inheritance, to use a new publishing flow for the current page and underlying or to not use a publishing flow at all for the page.
Settings
Inherit publishing flow
Inherits the publishing flow from above in the structure.
No publishing flow
Stops the inheritance of publishing flow from above in the structure.
Use publishing flow for this page and underlying
Stops the inheritance and you select a new publishing flow in the drop list.
Use selectable publishing flows for this page and underlying
Here you can add the flows that should be available for selecting on the pages. E.g. you might have several flows for a branch and the editor might want to choose which of the selectable flows to use. The publishing flow can also have authorization control.
Permission rights! This function requires the right "Manage publishing flows".