Erusin & Nisuin
A Jewish wedding ceremony consists of two separate components. The first component is referred to as the "erusin" or "kiddushin" which is translated as the "betrothal". The erusin is performed by the groom presenting his bride with a ring, or some other object of value, as he recites the sacred "harei at" formula in the presence of two witnesses. Although from this point onwards the couple is halachically committed to each other, and should they decide to break up they would require a Get, they are not fully married until the second component of the ceremony, the "nisuin", is performed. It is interesting to note that in ancient times there would often be up to a year interval between the "erusin" and the "nesuin" in order to allow for both sides to properly prepare all the necessary wedding arrangements.
There are two possible ways to perform the "nisuin". One way is simply to engage in intercourse for the express purpose of consummating the marriage. For a number of reasons, however, it is universal practice to only perform "nisuin" by a process called "chuppa" (not to be confused with the word used to describe a wedding canopy). "Chuppa" is defined as an act through which the couple demonstrates that they are now fully married. However, as we will see, it is quite unclear what actually constitutes "chuppa".
According to one approach, it is the yichud, spending time alone together after the wedding ceremony, which constitutes the "chuppa", and by extension, discharges the "nisuin" component of the marriage. Contrary to popular misconception, there is no need for the couple to cohabitate at this time, as the mere act of seclusion is enough to demonstrate that they are now married.
Other authorities argue that in order for the "nisuin" to take effect the husband is required to do something which demonstrates that he is taking responsibility for his wife, such as by feeding or clothing her. This is one of the reasons why it is customary for the groom to veil the bride before the wedding ceremony. Doing so is symbolic of his duty to provide her with clothing. In fact, the wedding canopy itself, which is usually constructed largely of cloth and upholstery, is also intended to symbolize clothing, and in this case, a shared garment. In some communities a tallit is used for the wedding canopy as it is a garment which features prominently in Jewish tradition. Eating together after the wedding ceremony, usually in the yichud room, is also considered to be an act of marital intimacy which qualifies for "chuppa" and "nisuin".
Finally, there is the view that "chuppa" is only fully discharged when the bride and groom enter their new home together. For this reason it is customary for the groom to welcome and escort his bride to the wedding canopy which is symbolic of the new home they will build together.
As a result of the many differing opinions as to what exactly constitutes "chuppa", common custom is to perform all of the actions mentioned above in order to leave no room for doubt.
While on the topic of "chuppa", it is worthwhile to mention the importance and meaning of holding the wedding ceremony under a canopy. It is taught that the wedding canopy is intended to be reminiscent of the tent of Avraham Avinu, which like a wedding canopy, was open on all four sides. Avraham Avinu constructed his home in this manner in order to make it more inviting and accessible for guests. Just as the wedding canopy symbolizes the home which the couple will create for themselves it also reminds them that guests must be a welcome and prominent part of their household.
The wedding canopy is also intended to recall the revelation at Sinai. This is based on the teaching that when God gave the Torah to the Jewish people, He held Mount Sinai above their heads like a wedding canopy. We are taught that even Adam and Eve were married under a chuppa.
 Ketubot 57a.
 Rambam, Hilchot Ishut 10:1; Aruch Hashulchan, EH 55:5.
 Rambam, Hilchot Ishut 10:1; Aruch Hashulchan, EH 55:14.
 Rambam, Hilchot Ishut 10:1,6.
 Chelkat Mechokek, EH 55:9; Aruch Hashulchan, EH 55:10.
 Yerushalmi, Sota 9:15.
 Taamei Haminhagim 963; Shulchan Ha'ezer 7:3:1; Ben Ish Chai, Shoftim 12.
 Aruch Hashulchan, EH 55:16.
 Rema, EH 55:1; EH 57:1; Aruch Hashulchan, EH 55:12.
 Aruch Hashulchan, EH 55:18.
 Beit Shmuel, EH 55:5.
 Some sources suggest that Iyov was also legendary for having his home open on all four sides. See Rashi to Avot 1:5.
 Shulchan Ha'ezer 7:3:3.
 Bava Batra 75a; Bereishit Rabba 18.