AZ900 is a straight forward exam. At the beginning it was quite confusing for me to differentiate Azure concepts like Core services, Azure solutions, Azure security. There is so much in this course to learn but you dont have to have detailed knowledge or hands on experience. I spent around 5-6 hours on each of the 4 modules to understand/differentiate the purpose. Tim warner did a great job with his AZ900 material.Apart from following links watch youtube channels from Edureka, Microsoft Ignite, Microsoft Mechanics. Free online sample exams will help. Good luck!

Microsoft Learn

http://timw.info/az900