You use upload stages to differentiate steps of the overall upload process.

You assign upload stages to process steps in Customizing for Cross-Application Components under  Demand Data Foundation Data Upload Define Processes and Steps .

In most cases, the usage of upload stages is optional. In case of manual upload, the upload stage has to be set specifically.

If you want to use the same data delivery agreement for a manual upload as you have used for an automatic upload with the folder scanner, you have to define upload stages in Customizing for Manual Data Upload.