AZ-900 certification from Microsoft Azure is the fundamental certification offered by Azure, to validate your foundational knowledge on the Azure cloud service. This is created to help you equip with the necessary knowledge in Azure like Azure services, Azure Workload, Azure security and other concepts of networking, compute, storage, and application development. This certification should be considered as the requirements of any specific further role-based certifications (like for Architects, developers, etc.).
You could take this exam to get started with the knowledge on this cloud domain especially Azure. If you are new to the cloud computing arena and wish to get started, consider enrolling in a good Azure fundamentals certification course from a reputed institute. Watch the following video on Microsoft Azure Fundamentals Certification.