In ancient days, there prevailed gurukul system, where the boy goes to live with his guru to acquire knowledge and expertise. This stage is Brahmacharya or studenthood for the boy and he would be eligible to get married only once he completes his studies that is brahmacharya and this form of marriage is named Brahma Marriage. Once he is ready to get married after acquiring all the expertise required his parents would approache the family of a matching and eligible girl.
The father of the girl also carefully chooses the bridegroom who is well versed in Vedas and of a noble character. This is how a Brahma marriage was arranged. The girl`s family didn`t have to give any dowry to the boy`s family. There was the ritual of kanyadaan which symbolizes that the father gifts his daughter to the boy. In this system of marriage no commercial transaction is done. Among the eight types this is regarded as the highest type of marriage by the dharmashastras.
This marriage is performed even before the girl is attained her puberty. The mantras are chanted while performing the marriage, which are addressed by the groom to the bride who comes to him. It was understood that a girl`s marriage, which has same significance for her that the upanayana has for a boy, must be performed when she is seven years old (or eight years from conception).