As with most services on a router, you must configure the specific service that you want because by default no functionality is provided. To use AAA on a router, you must not only define the AAA commands, but you must also tell the router where to find the AAA server. You can also configure authentication without configuring, and therefore using, authorization and accounting. If you want to configure authorization, you need to configure authentication.
Your first step in configuring AAA must be to enable the AAA daemon on the router. If you do not enable the AAA daemon, you cannot configure any AAA services.
The command to enable the AAA daemon is easy:
Router(config)# aaa new-model
The AAA daemon ...