There is no free version of Tableau available, except Tableau Public and Tableau Reader which is available for free for the public to open, create and interact with data visualizations. Whereas, Tableau Desktop is free for full-time students only.
In general, Tableau offers the Tableau Desktop version freely for a trial period of 14 days, post which you need to pay the licensing fee for continued usage. It costs monthly $35 for Tableau Desktop personal and $70 for Tableau Desktop professional.
If you are interested in getting trained and certified in Tableau, I would recommend you to take up the Tableau certification course which is a 30hrs instructor-led or self-paced course with 32hrs of projects to get sufficient hands-on experience.
Additionally, watch our YouTube video on Tableau training for beginners to help you get started.