2:   What does "M-x command" mean?
  
  "M-x command" means type M-x, then type the name of the command, then
  type RET.
  
  M-x (by default) invokes the command `execute-extended-command'.  This
  command allows you to run any Emacs command if you can remember the
  command's name.  If you can't remember the command's name, you can type
  TAB and SPC for completion, and "?" for a list of possibilities.  An Emacs
  "command" is any "interactive" Emacs function.
  
  NOTE: Your system administrator may have bound other key sequences to
  invoke execute-extended-command.  A function key labeled `Do' is a good
  candidate for this.
  
  To run non-interactive Emacs functions, see question 53.