Catalyst 2960-X Switch Security Configuration Guide, Cisco IOS Release 15.0(2)EX[1]
You have to enable privileged EXEC mode and enter the global configuration mode.
Switch(config)# aaa new-model Switch(config)# radius-server host <imRAD IP address> auth-port 1812 acct-port 1813 key <shared secret> Switch(config)# aaa authentication login default radius local Switch(config)# aaa authorization network radius Switch(config)# aaa authorization exec radius Switch(config)# aaa accounting network start-stop radius Switch(config)# aaa accounting exec start-stop radius