AAA Authentication on Cisco IOS

I have this configuration on my router please can you help to understand? my intial understanding as below:
! this is aaa Authentication password Prompt if the Tacacs Authentication if it’s failed (meaning with tacacs Authentication this is not showing)
aaa authentication password-prompt Backup_Authentication_Password:
! this is aaa Authentication user Prompt if the Tacacs Authentication if it’s failed (meaning with tacacs Authentication this is not showing)
aaa authentication username-prompt Backup_Authentication_Username:
! this is will let the switch first use an external aaa server with tacacs+ protocol then will use local
aaa authentication login default group tacacs+ local
! Enable authorization on the console through aaa server (it’s disabled by default on the console)
aaa authorization console
! Enabe Authorization through aaa server to configure mode on the router
aaa authorization config-commands
! All authorization VTY or Console or for configure mode will use local then aaa external server
aaa authorization exec default local group tacacs+
! All these levels below will use aaa external and also the commands will be defined in aaa server
aaa authorization commands 0 default local group tacacs+ if-authenticated
aaa authorization commands 1 default local group tacacs+
aaa authorization commands 15 default local group tacacs+

Also I have question in authorization server configuration what need to be done for each Authorization line to be working as expected?

Thanks,
Samer Abbas