https://en.myjyotish.com/en/astrology-blogs/chanakya-niti-these-remedies-will-solve-all-your-problems-be-it-big-or-small
Method of Kharna-
On this day, after taking a bath in the morning, clean clothes should be worn. Women and Chhath Vratis apply vermilion from nose to forehead. On the day of Kharna, fasting women keep fast throughout the day and in the evening prepare prasad by making rice and jaggery kheer on a wooden stove. After worshiping the Sun God according to the rituals, the fasting women accept this offering. This prasad is also distributed among other family members. After consuming this prasad, 36 hours of Nirjala fast of fasting women begins. According to religious beliefs, Chhathi Maiya enters the house only after Kharna Puja.
Importance of Kharna–
There is a tradition of making offerings of Chhath Puja on the day of Kharna. The prasad is made in a very pure way. After the kharna, the prasad is made on the new chulha. On the day of Kharna, fasting women take food only at one time.
https://en.myjyotish.com/en/astrology-blogs/please-shanidev-on-saturday