Have you tried reading this article?
Tableau Online is still a paid service from Tableau. The only free option to publish your own content is Tableau Public.
Hope this helps!
Consider the following:
With Tableau Desktop you develop and your reports are published in Tableau online (Cloud) or Tableau Server (on premise). These are all paid versions
Then there is Tableau Public for free. Once again you develop on your desktop and publish in de cloud. The available supported datasources is limited (Excel, textfile, Access, Statisical file and Odata, Web data connector. Please realize there is no authorization concept available. So all data is available for everybody who is viewing Tableau Public. For journalist its a great feature:)