It is only possible to export and publish a Workflow if there are no validation errors. These are displayed at the bottom of the main screen. The associated step in the Workflow will also be highlighted. In this example one of the Decision Steps is not labelled or connected.
Once you have fixed any errors you can manually validate the Workflow again to double check that everything is ok.
If there are no errors, you can publish your completed Workflow by clicking on the File Menu and selecting Export Zip.
Give the Workflow a name and save it locally on your drive. To upload the Workflow zip file follow the instructions here.
Publishing Your Workflow