The Cisco networking Internetwork Operating System (IOS) has a great context-sensitive Help function, which means the IOS can help you find the specific item you are currently working with.

To start using Help, you need to type a command in the CLI. After you type one command, you can ask the IOS for help with possible options for that command. After you type your selected command, type a space and a question mark to get a list of options for that command. For example, running the copy command with the question mark results in the following:

Router#copy ?
  /erase          Erase destination file system.
  /noverify       Don't verify image signature before reload.
  /verify         Verify image signature before reload.
  cns:            Copy from cns: file system
  flash:          Copy from flash: file system
  ftp:            Copy from ftp: file system
  http:           Copy from http: file system
  https:          Copy from https: file system
  null:           Copy from null: file system
  nvram:          Copy from nvram: file system
  pram:           Copy from pram: file system
  rcp:            Copy from rcp: file system
  running-config  Copy from current system configuration
  scp:            Copy from scp: file system
  startup-config  Copy from startup configuration
  system:         Copy from system: file system
  tftp:           Copy from tftp: file system

In fact, if you have not typed anything on the CLI, you can still type the question mark to get a list of all the available commands that you can use from your current mode. This is a very long list, so if you start with the first few letters of the command, you will greatly reduce the size of the list.