The Mitzva of peryia veribyia "be fruitful and multiply" is achieved when one has a son and daughter (see here) but it is fully completed only when we have grandchildren: a grandson and a granddaughter from two of our children (shulchan 'arukh, eben ha'ezer, 1:6). Part of the Mitzva of peryia veribyia, therefore, consists in the parents helping their children to get married. In this way the parents are partners with their children in fulfilling the first Mitzva of the Tora.
How do parents help their children? The parents help throughout the life of their children, raising them to be honorable and respectable individuals, and investing in their Jewish and professional education. A good education enables our children to marry with a suitable spouse, and provides them the means and techniques to maintain themselves. Parents also help their children providing them counseling and advise about dating and marriage. When the time comes, parents should be willing to help their children financially with the expenses of the wedding, obviously, according to what the parents can afford. They should also be willing to assist their children in the initial steps of their new life, according to the needs of the new couple and to what parents can afford.
Similarly, every Jew should be willing to help the needy and poor when they want to get married. One of the most important forms of Tzedaqa, considered a category by itself, is the Mitzva of hakhnasat kalla: helping an orphan or needy bride (or groom) to get married. It is a very special merit for individuals and for a community, to assist financially a bride or a groom with insufficient means, to get married. According to the shulchan 'arukh (yore de'a 249:15) hakhnasat kalla, takes precedence over all other types of Tzedaqa.