Why does tableau makes it very difficult to access the program to practice the skills? I find it very hard just to access the program just to practise

sounds like you are frustrated - but actually there are several options - first the FREE ones Tableau Public - you can hide what create if you don't want it shared in public, next the Salesforce Trailhead https://trailhead.salesforce.com/content/learn/trails/become-a-data-driven-team-using-tableau is a guided training site and then there are the Accelerators and Sample workbooks

and the subscription-based e-learning site https://www.tableau.com/learn/training/elearning