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 3 if you don't know how.)