I am currently at the Using Joins in Tableau lesson, and when downloaded to Tableau the two data files (audiobook sales and reviews one) cannot be merged together, and are not behaving as shown on the video, even if following the exact same steps as the instructor. I believe that is due to the fact that the course does not work with the most updated version of Tableau, like I am doing, so the settings are completely different and the method to merge data is also different. I believe it is past the time to give this part of the course some attention, I am sure that every student who finally gets to learn the basics about Tableau would be very disappointed to be surprised by a video that teaches you using an older version of the tool.
I found this page saying how Tableau has changed the Join function if you were interested https://help.tableau.com/current/pro/desktop/en-us/datasource_datamodel_whatschanged.htm. Tableau also offers free lessons https://www.tableau.com/learn/training/20202 which may help us with joins and relationships