Hi @Ken , welcome to Microsoft Q&A forum.
SQL Server Always on feature talks about high availability of the database and also talks about how to recover in case of database failure. With Azure SQL Database and Azure SQL managed instance these features are already available as part of high availability models and failover groups. Please refer to below document that talks about these features in details:
High availability for Azure SQL Database and SQL Managed Instance
Use auto-failover groups to enable transparent and coordinated failover of multiple databases
For migrating on-premise SQL Server to Azure, its good to know each and every details but in real time even if we don't need to go through these minute details it is totally fine as we have already available detailed documentation that has step by step process of migration from on-premise to Azure.
Azure SQL Managed Instance:
In this article, you can check Azure Database Migration Service as an example to check the migration process. There are other ways as well. Please check the versions supported before you choose any option here.
Azure SQL:
SQL Server database migration to Azure SQL Database
Please check these links and let us know if you have any queries related to this, or if you face any issues while migrating. These documents are bit lengthy, but we are there to assist you in case of any questions.