Transport Layer Security (TLS) which was previously known as Secure Sockets Layer (SSL) is used for securing web servers by encrypting web traffic. In Azure virtual machine, these TLS/SSL certificate is stored in Azure Key Vault that cryptographic keys and secrets, such as certificates or passwords. Azure Key Vault helps for secure deployments of these certificates to Linux VMs of Azure.
If you want to learn Azure, I would recommend this course on Azure Certification by Intellipaat which has experienced instructors, best curriculum, and projects.
Also, watch this video on Azure Virtual Machines: