When our friends are having a birthday, achieving a success  or in ajoyful situation, we should congratulate them. We can also give them good wishes and prayer to a good relationship. Congratulation is an  expression that is used to congratulate others for their fortune and achievement. The social function of congratulations is to congratulate someone for her fortune and achievement in order to  keep good personal relationship.  The expressions of hope and wish are used to convey our hopes or wishes to others.