1: What do these mean: C-h, M-C-a, RET, "ESC a", etc.?

  C-x: press the `x' key while holding down the Control key

  M-x: press the `x' key while holding down the Meta key (if your computer
       doesn't have a Meta key, see question 125)

  M-C-x: press the `x' key while holding down both Control and Meta
  C-M-x: a synonym for the above

  LFD: Linefeed or Newline; same as C-j
  RET: Return, sometimes marked Enter; same as C-m
  DEL: Delete,  usually not the same as Backspace; same as C-? (See
       question 121 if deleting invokes Emacs help)
  ESC: Escape; same as C-[
  TAB: Tab; same as C-i
  SPC: Space bar

  Key sequences longer than one key (and some single-key sequences) are
  inside double quotes or on lines by themselves.  Any real spaces in such
  a key sequence should be ignored; only SPC really means press the space
  key.

  The ASCII code sent by C-x (except for C-?) is the value that would be
  sent by pressing just `x' minus 96 (or 64 for uppercase `X') and will be
  from 0 to 31.  The ASCII code sent by M-x is the sum of 128 and the ASCII
  code that would be sent by pressing just the `x' key.  Essentially, the
  Control key turns off bits 5 and 6 and the Meta key turns on bit 7.

  NOTE: C-? (aka DEL) is ASCII code 127.  It is a misnomer to call C-?  a
  "control" key, since 127 has both bits 5 and 6 turned ON.  Also, on very
  few keyboards does C-? generate ASCII code 127.

  For further information, see "Characters" and "Keys" in the on-line
  manual.  (see question 3 if you don't know how.)

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