Earlier, Tableau prep was coming included with Tableau Desktop as they both were separate offering separate services. But now Tableau has combined them into one and are offering them both in the Tableau creator and also in Tableau Server.
Want to join a Tableau training course, then I would recommend you to take up the Tableau certification course from Intellipaat, which has an added benefit of making you prepared for the Tableau Desktop Qualified Associate certification exam.
Also, do watch our YouTube video on introduction to tableau which will help you get started.