Importance of making and sharing merit What are the benefits of transferring karmic fruitfulness and how is this done by Buddhists?
Make merit is the core of the buddhist practice and is done by being resolute and practice deeds (through mind, speach and body) of generosity, renunciation and goodwill. This will gradually lead to the decrease of the defilements (greed, ill-will and delusion) and to the maturation of the eight factors of the Noble Eightfold Path. 

Sharing of merit is one of the Ten ways of Making Merit because is a expression of goodwill and generosity and is done by inviting others to rejoice in the merits that you have done (which by itself is also a source of merit) or be intended that they do so. In other words, the more you practice merits, the closer you are to Nibbana. If you hold the intetion that others also make merit by rejoicing with your merits, this means that you are resolved in goodwill and generosity (which is right view/right resolve), thus, this is again a souce of merit.


  May all beings  —  without limit, without end  —  have a share in the
  merit just now made,  and in whatever other merit I have made.
  
  Those who are dear &amp; kind to me  —    beginning with my mother &amp; father 
  —     whom I have seen or never seen;     and others, neutral or hostile;
  
  If they know of my dedication of merit,   may they themselves rejoice,
    And if they do not know,    may the devas inform them.
  
  By reason of their rejoicing  in my gift of merit,    may all beings
  always live happily,  free from animosity.
  
  May they attain the Serene State,     and their radiant hopes be
  fulfilled.
  
  Dedication of Merit