FTP in ABAP

call function 'FTP_CONNECT'
  exporting
    user            = user
    password        = pwd
    host            = host
    rfc_destination = dest
  importing
    handle          = hdl.

<b>What is Handle ?</b>

 call function 'FTP_COMMAND'
    exporting
      handle        = hdl
      command       = cmd1
      compress      = compress
    tables
      data          = result
    exceptions
      command_error = 1
      tcpip_error   = 2.
  loop at result.
    write at / result-line.
  endloop.
  refresh result.

<b>What is result? Why do we display it?</b>

Could some one explain me exception handling. I am new to ABAP and dont quite understand how to call function modules. What does command_error = 1 and tcpip_error = 2 mean?