Karva Chauth is observed by married women (suhagini) for ensuring wedded bliss and wishing long life for their husbands and children. A married woman who observes this vrat is called ‘Saubhagyavati’ (joyous and happy state of wifehood).
On the occasion of this vrat (Fast) a kalash (small container) is filled with either milk or water. In that kalash is placed Pancha Ratna (five pieces of different metals gold, silver, copper, brass and iron). The kalash is then presented to a Brahmin and also exchanged with other married women. While thus presenting the kalash, a wishful prayer is offered to Lord Ganesh: "Let the offerings of this Karva (Karak (gift bring long life to my husband and may my saubhagya be everlasting". And express such desire that ‘May my death precede that of my husband so that I can enter the chitaa (funeral pyre) as a bride (not as a widow).
This katha (narrative) first took place between Siva and parvati. Siva told Parvati about the significance of Karva Vrat. In Dwapar Yuga, Draupadi asked Lord Krishna about the vrat of Karva Chauth. Thereafter, the very first time this vrat was observed in the town of Shukraprastha by Veeravati, the daughter of Vedsharma and Leelavati. Ever since this vrat has been observed by married women till the present day.
On the occasion of Karva Chauth which is on the day of Kartik Krishna Chaturthi, fasting (vrat) is observed. In the evening, after taking a bath, under a banyan tree (or in the absence of such tree, draw a picture of such tree) place murtis or pictures of Siva, Parvati, Ganesh and Kartikeya and do puja ceremony (shodashopachar or sixteen step puja ceremony). Then for the offerings of arghya (rice, flower etc.), while waiting for the moon to rise, japa is done with the mantra "Om namah Shivaya". Havan (sacred fire ceremony) is also done. Thereafter, having sited the moon, offer the arghya.
If the husband is present, then worship him with Panchopchar or gandh, pushpa, dhoop, deep and naivedya (perfume, flower, incence, lamp and food). If the husband is away on travels, then offer a prayer to Almighy to grant long life to your husband. Thereafter bring the vrat to its conclusion.
Lord Krishna urged Draupadi to observe the vrat of Karva Chauth so that through its influence Arjuna can defeat the Kauravas on the battlefield and acquire back the kingdom.
Married women who thus offer wishful prayer for saubhagya by observing the Karva Chauth Vrat, acquire saubhagya, progeny and lasting prosperity.
Later on sumptuous dinner is served as a part of the celebration.