Hi Herman,
Welcome to the forum!
Great feedback from Brian and I must agree with him: There are no beginner books.
When I started, I was looking for similar material as well. Sharing my experiences:
- What was really valuable to me was the official Microsoft video series about Power BI ( https://www.youtube.com/playlist?list=PL1N57mwBHtN0JFoKSR0n-tBkUJHeMP2cP). This training guides you to the whole process in short “easy to digest” videos
- The content on EDNA. The starter course on Enterprise DNA is a fabulous starting point as well.
- The forum here: Don’t hesitate to ask a question here. Add your .pbix to your post , discuss what you want to do and surely somebody here will help you.
I can also recommend the Definitive Guide to DAX that Brian recommended ( I do not know the other book 
), but I would not suggest this as a first course. It would be the same as learning a new language (for example Spanish) by reading a dictionary. Reading the dictionary will not teach you the language! 
Have a great evening!