Cisco IOS "help" and "show" options available at the USER MODE prompt:

Cisco Internetwork Operating System Software
IOS (tm) C2600 Software (C2600-I-M), Version 12.2(12k), RELEASE SOFTWARE (fc1)

Router>help

Help may be requested at any point in a command by entering
a question mark '?'.  If nothing matches, the help list will
be empty and you must backup until entering a '?' shows the
available options.
Two styles of help are provided:
1. Full help is available when you are ready to enter a
   command argument (e.g. 'show ?') and describes each possible
   argument.
2. Partial help is provided when an abbreviated argument is entered
   and you want to know what arguments match the input
   (e.g. 'show pr?'.)


Router>show ?
  backup         Backup status
  c2600          Show c2600 information
  cca            CCA information
  cdapi          CDAPI information
  cef            Cisco Express Forwarding
  class-map      Show QoS Class Map
  clock          Display the system clock
  compress       Show compression statistics
  connection     Show Connection
  controllers    Interface controller status
  cops           COPS information
  dialer         Dialer parameters and statistics
  exception      exception informations
  flash:         display information about flash: file system
  history        Display the session command history
  hosts          IP domain-name, lookup style, nameservers, and host table
  ip             IP information
  isdn           ISDN information
  location       Display the system location
  modemcap       Show Modem Capabilities database
  policy-map     Show QoS Policy Map
  ppp            PPP parameters and statistics
  qdm            Show information about QoS Device Manager
  queue          Show queue contents
  queueing       Show queueing configuration
  radius         Shows radius information
  rmon           rmon statistics
  rtr            Response Time Reporter (RTR)
  sessions       Information about Telnet connections
  snmp           snmp statistics
  tacacs         Shows tacacs+ server statistics
  template       Template information
  terminal       Display terminal configuration parameters
  tgrm           Trunk Group Resource Mananger info
  traffic-shape  traffic rate shaping configuration
  users          Display information about terminal lines
  version        System hardware and software status