You have to learn managing Azure resources and Storage, handling Virtual machines and identities to pass the AZ-103 exam. Keep following online resources and study groups in learning these concepts. Learning all these topics on own could be difficult. So, enroll an online course with a good curriculum and instructor-led-training.
I strongly recommend this Microsoft Azure Training by Intellipaat that covers all the topics required to pass the AZ-103 exam.
You can watch this video to know more about the Azure Administrator AZ-103 training course of Intellipaat: