Here is your short paragraph on Karwa Chouth:
Karwa Chouth falls in the month of Kartik (October—November) and married women observe vigorous fast.
In the morning after taking bath, they dress up in new clothes and collect various articles including a Karwa (an earthen pot with a spout) decorated with coloured rice and then offer worship to Lord Shiva and Parvati.
They pray for the longevity and prosperity of their husband. On the floor of the house, women draw sketches of the Sun, Moon and Karwa. At night when the moon appears, flowers are offered in worship and the day-long fast is broken.
In the lunar month, which occurs between October 15 and November 14, women from the northern India undertake two fasts on the fourth and eight days of the waxing moon. As said, Karwa Chouth involves vigorous fast for the whole day until they see the moon. The rite is performed for the well-being of the husband.
Myth tells as that a princess of royal blood observed a fast on this day, but in the evening she heard news of her husband’s demise. She went to her husband’s place lamenting her fate when Goddess Parvati met her on the way.
Moved by the entreaties of the princess, Goddess Parvati pricked her finger and gave some blood to the princess. On her advice, the princess anointed the body of her husband with this blood and the dead man came back to life. The day has been celebrated as an auspicious day ever since by married women.