The Azure SQL Database Offline Migration Wizard – does it disable my source db when i start migration

I have SQL server on Azure VM. I have setup the azure database migration services. I am on the last step of the wizard where it says in the documentation downtime starts when I hit start migration.

Does it mean that it will destroy, or put the source sql server readonly or offline somehow? Does it simply mean that my application will need reconfiguring to point to the new copy of the database, so for consistency, stop writing to the source database?

I want to test, so I would like the migration to copy the database over so I can use a test copy of the application on the migrated data. When I am satisfied, I aim to cease connections to the source database, complete the migration, reconfigure the application so it runs on the new Azure SQL database.

Should I be doing this another way? I cannot quite read in the documentation what is happening.