The sections are broken down as follows:

CST6CDT   The timezone of and if DST is used in this TZ
  CST   Central Standard Time
  6   The (hour) offset from GMT/UTC
  CDT   Central Daylight Time
M3.2.0/2:00:00   The time when DST begins (when we shift)
  M3   The third month (March)
  .2   The 2nd occourance of the day (next item) in the month
  .0   Sunday
  /2:00:00   Time of day to change
M11.1.0/2:00:00   The time when DST ends (when we shift back)
  M11   The eleventh month (November)
  .1   The 1st occourance of the day (next item) in the month
  .0   Sunday
  /2:00:00   Time of day to change