After a young man has to completed his gurukulavasa and performed the samavartana he has to wear a "double sacred thread". He must discard the marks of his student-bachelorhood - the staff, the antelope skin, the girdle - and wear the pancakaccha and an upper cloth. As a celibate-student he was not permitted to use any footwear; he could not also adorn himself with sandal-paste, ear-studs and flowers. He may now even darken his eyes with lampblack. Adorning himself and putting up his umbrella he must approach the king or a royal representative. The latter must be impressed by his learning and the quality of his brahmacarya. The young must acquire [from the king or the royal representative] money and material as a gift for his marriage, so say the sastras.
One point that emerges from this is that the marriage expenses are to be borne by the groom or his parents. A second point is that a young man who has had samavartana must wear the "double sacred thread" and pancakaccha even if he remains single. One's strength or potency is preserved by wearing a cloth whose ends are pleated, or made into folds, and tucked in. Muslims have the end of the cloths sewn together. Even people who do not belong to the twice born caste - except in Tamil Nadu and Kerala - tuck in their dhotis or vestis, not to speak of pancakaccaha. (Today even when they come to see me people come in trousers. That being the case it is ridiculous or meaningless to speak of differences between the two types of wears).
In these days there is neither gurukulavasa nor samavartana nor the pilgrimage to Ganga. But there is an extra "item" in weddings called "Paradesi-k-kolam" just to extort money or gift from the bride's family. The groom is presented with an umbrella, a pair of sandals and a walking stick. A ceremony called "kasiyatra" (the pilgrimage or journey to kasi) is conducted in which groom darkens his eyes with lampblack and wears a gold chain.
Those who do not marry and remain "naisthika brahamacarins" (lifelong brahamacarins) are exceptions to the rule that no man ought to remain even a single moment without belonging to one of the asramas. That is after the proper conclusion of his student-bachelorhood he has to prepare to become a householder.
The Brahmin is born with three debts: he owes a debts to the sages, to the celestials and to the fathers. He repays the first by learning the Vedas as a student-bachelor; the second by taking a wife and performing sacrifices; and the third by begetting a son. So without marriage he cannot repay the second and third debts.
Sons are primarily intended for the repayment of the debts to the fathers. Performing the sraddha ceremony is not enough. Forefathers of the past three generations are to be made to ascend from the manes. So even after a man dies, for two generations the daily libations must be offered to him. That is why the birth of a son is considered important. (The case of the naisthika brahmacarin and the sannyasin is different. Because of their inner purity and enlightenment, they can liberate, not just two generations, but twenty-one generations fathers without performing any sraddha ceremony).
Panigrahana (the groom taking the hand of the bride in his), mangalyadharana, saptapadi (the bridal pair taking the seven steps round the sacrificial fire ) are important rites of the marriage function. There is a controversy about whether or not mangalya-dharana is a Vedic rite. It is an unnecessary controversy. Mangalya-dharana is a custom that is thousands of years old and it is an essential part of the marriage samskara.
As I said before, after completing his student-bachelorhood a young man must take a wife for the pursuit of dharma. The latter should dedicate herself to him so as to become pure within. The purpose of marriage is a life of harmony and the procreation of virtuous children.
Grhasthasrama is called illaram in Tamil and it is extolled by the wise in the Tamil country also. "Grha" means a house. A young man who returns to his house from the guru's and practises dharma is a "grhastha". One who resides in a house, a grha, is a grhastha. The Tamil wife calls her husband "ahamudayan", "ahattukaran", "vittukaran": these terms have to do with the house or the home. Only the wife can refer to her husband thus, not others. She herself is called "grhini", not "grhastha". The latter would mean no more than "one who resides in a house". But "grhini" means the house belongs to her (the wife), that she manages the household. The husband is the illaratan in Tamil and it means one performs the dharmic rites in the house, "il-arattan". The wife is "illal", one who owns the house.
The husband is not called illan (illan, as it happens, means one who does not possess anything or one who is indigent). The wife is also called illattarasi (queen of the house), "manaivi"(owner of the house), or "manaiyal"; but the husband does not have similar appellations like "illattarasan"(king of the house), "manaivan" or "manaiyan"(owner of the house). In Telugu the wife is called "illu" (corresponding to the illal of Tamil).
For a general background, please see here