What they mean is that on a standard german keyboard layout to type []{}~ one would press

  [ Alt Gr-8
  ] Alt Gr-9
  { Alt Gr 7
  } Alt Gr 0
  ~ Alt Gr +

While on an Apple keyboard you use

  [ ⌥-5
  ] ⌥-6
  { ⌥-8
  } ⌥-9
  ~ ⌥-n