Can someone help explain Liga MX rules?

Every season, The 18 teams are split into three groups of six, either group one, group two, or group three. They remain in their respective groups throughout the two tournaments played that season. The qualification phase of the tournament lasts 17 weeks, as all teams play each other once per tournament in a home and home series over both tournaments. The qualifying teams reach the liguilla phase of the respective tournament. As of June 7, 2011 the League has decided to do away with the 3 groups and allow the top 8 to directly qualify to the "Liguilla" phase of the tournament, thus eliminating the 'Repechaje' match when a 4th place team from one group had more points than the third place team from a different group, along with that, they also changed who the qualifiers from the Apertura would be for the 2012 Edition of the Copa Libertadores, which would be the top 3 team who are not qualified for the Concacaf champions league or Conca-champions as the tournament is called.