The chuppah is a tapestry attached to the tops of four poles. The word chuppah means covering or protection, and is intended as a roof or covering for the bride and groom at their wedding.
The chuppah is not merely a charming folk custom, a ceremonial object carried over from a primitive past. It serves a definite, though complicated, legal purpose: It is the decisive act that formally permits the couple's new status of marriage to be actualized, and it is the legal conclusion of the marriage process that began with betrothal. Together these two kinyanim (acts of acquisition) are called chuppah ve'kiddushin.
Chuppah symbolizes the groom's home, and the bride's new domain. More specifically, the chuppah symbolizes the bridal chamber, where the marital act was consummated in ancient times.
The tapestry canopy that we know as chuppah was first identified by Rabbi Moses Issereles (Rema) in the sixteenth century, and we must assume that it was relatively new in his time. The concept, however, is ancient, and the Talmud considers it biblically required for marriage.
What exactly is chuppah? Although we do know that originally it was the groom's home, or an addition to his father's home into which the new couple moved, we cannot know, in precise halakhic terms, what the symbol of that chuppah is supposed to be today. (Psalm 19:6 speaks of the bridegroom emerging from his chuppah, while Joel 2:16 says, "Let the bridegroom emerge from his chamber [chedro], and the bride from her chuppah.")
According to several of the medieval scholars, notably Ran and Rif, chuppah was effected by the bride's mere entrance into the groom's home. That is why the symbolizing of the chuppah in a synagogue or hall, for example, can be done with only a canopy; if it had walls, then as soon as the couple stepped into it after the betrothal with the intent of marriage, they would change status. Maimonides held that it was only in seclusion, yichud, that the chuppah sealed marriage. Tur felt that the groom covered the bride with an article of clothing, and that was the legal chuppah act. Nachalat Shivah quotes the authoritative Ashkenazic custom that a tallit over both their heads was the definitive chuppah. The Tosafists stated that the covering of the bride's face with a veil finalized the marriage. Mordecai taught that the very process of leaving her father's home to enter the groom's home was itself chuppah; others, such as Rosh, held that the decorated hand-carried coach, which in the days of the Second Temple transported the bride through the city, was really the chuppah. The "Bach," therefore rules that we perform virtually all of these acts in order to cover all halakhic possibilities. The bride is veiled, and the overhead canopy is the groom's covering for the bride. The beautiful ancient Askhenazic custom of placing the groom's tallit on the couple's head for the nuptial blessings has been retained largely by Sephardim and German Jews.
The construction of the chuppah is simple: a cloth or tallit is spread over four poles. Care should be taken, if at all possible, that the cloth be fastened to the top of the poles (rather than to their sides), which serve as a legal separation and wall. Legally, this constitutes a private domain in regard to the laws of the Sabbath, and it transforms the chuppah, technically into the groom's private home.
What sort of cloth should be used for a chuppah? Historically, the chuppah was a desirable object of art, which everyone sought to decorate - after all, it also symbolized the covenantal marriage of G‑d and His people. The medieval community often used a parokhet (an Ark covering), although it was felt to be inappropriate to apply an object of sanctity to the bridal chamber. Considering the suggestion that the cover be affixed to the top of poles, a floral chuppah is not desirable, although it is perfectly acceptable to cover and decorate the tapestry chuppah with a canopy of flowers. Perhaps genuine beauty resides in simplicity. How much more elegant is the symbol of a tallit attached at the top of four portable poles held by four friends!
The chuppah is required only for the nuptials, but with today's elaborate chuppot, one cannot help but have the entire service, even the betrothals, under the chuppah. That is perfectly acceptable, but it would be more significant, and also more instructive to an unknowing audience, to raise a portable chuppah after the reading of the ketubah, in time for the seven blessings of the nuptials.
The bride and groom must stand under the chuppah. It is not necessary for rabbi, cantor, witnesses, or parents to be under the canopy. If their presence were a requirement, the other symbols of chuppah—veil, tallit, clothing, privacy—would not be effective without them.
The chuppah is a legal instrument, but the fact that only this canopy symbol survived makes a statement to the couple. First, it teaches that this simple, fragile roof, which is now common to both partners, launches the marriage. In the words of William Henry Channing, it teaches them "to live content with small means: to seek elegance rather than luxury, and refinement rather than fashion, to be worthy not respectable, and wealthy, not rich." Second, it affirms the teaching of Ha-manhig that the chuppah sets the couple apart from the crowds, to avoid it appearing as though they were "marrying in the marketplace," which was considered gross and indelicate in the extreme. Marriage is the establishment of a home, an island of sanity and serenity "far from the madding crowd."
Source: Lamm, Maurice. “The Bridal Canopy (Chuppah),” Chabad.org.