RE: "still not able to do this." Please clarify. Are you getting an error message?
As per instruction "Select Add and navigate to where your .bak file is located. Select the .bak file and then select OK.", note that the the .bak file must be accessible to the SQL Server instance, not just your local machine running SSMS. If SQL Server is running on a different machine, the file must be on a drive that the server can access, such as a local drive on the server or a network share with proper permissions.
Copy the .bak file to a location on the SQL Server.
Very simple. Install SQL management studio, connect to the old database server. Backup the database using backup option. Connect to the new server, restore the database there. If you are unsure let me know, I would be happy to help.