Here’s a thread with some resources that I think you’ll find very helpful in mastering the use of variables. Understanding proper use of variables is one of the absolutely fundamental skills necessary to write anything more than basic DAX code.
In addition to studying these resources, I 100% agree with @AntrikshSharma that practice and more practice is the key. Through initiatives like Problem of the Week and the Data Challenges, we offer a lot of different opportunities for that structured learning and practice. In addition, you can learn a great deal by reading DAX -related forum posts (I literally learn something new about DAX from every @AntrikshSharma post) and also attempting to solve other peoples’ DAX problems , whether you post a solution or not.
https://forum.enterprisedna.co/t/which-enterprise-dna-course-to-master-dax-variables/5837/2?u=brianj
I hope this is helpful. Good luck with your study.
– Brian
P.S. I also used to think the goal was learning to write long, complex DAX. I now realize the better goal is to write the shortest, simplest DAX that will solve your problem. The way to do that is often not to write DAX at all, but to focus first on structuring your data and performing necessary calculations and transformations in Power Query. The lesson I learned is that you need to have a balanced study plan, advancing your skills equally in both tools.