Lakshmi Puja is a Hindu religious festival that falls on Amavasya (new moon day) of Krishna Paksha (dark fortnight) in the Vikram Samvat Hindu calendar month of Ashwin, the third day of Tihar or Deepawali.
According to legend, Lakshmi, the goddess of wealth and Vishnu‘s wife, visits her devotees and bestows gifts and blessings upon each of them. To welcome the Goddess, devotees clean their houses, decorate them with finery and lights, and prepare sweet treats and delicacies as offerings. Devotees believe the happier Lakshmi is with the visit, the more she blesses the family with health and wealth.
Lakshmi Puja, or the worship of the goddess of wealth, is the main event of Diwali in North and West India. It is popularly believed that Lakshmi likes cleanliness and will visit the cleanest house first. Hence, the broom is worshiped with offerings of haldi (turmeric) and sindoor (vermilion) on this day. Lamps are lit in the evening to welcome the goddess as they are believed to light up her path. On this day, a supported light of knowledge is said to dawn upon humanity. This self-enlightenment is expressed through the twinkling lamps that illuminate the abode of the worshippers. It is believed that on this day, the goddess walks through the green fields and loiters through the by-lanes and showers her blessings on mankind for glory and prosperity.
With pomp and ceremony, Lakshmi is invited into the homes of devotees to partake of the gifts that are a part of the puja. The most auspicious time for the puja is decided when amavasya tithi prevails during pradosh kaal or the evening time. On this day, the sun enters its second course and passes the constellation Libra, which is represented by the balance or scale. Hence, the sign of Libra is believed to suggest the balancing and closing of account books.
(source:https://en.wikipedia.org/wiki/Lakshmi_Puja)
How do we celebrate it:
On the evening of this day, after cleaning the house we make rangoli and light diyas. We arrange our jewelry in front of God and we also keep some cash there. We arrange the idols of Goddess Laxmi and then perform Aarti and Pooja. We offer prashad – lahya and battase and pedhas and distribute it to the family after the pooja is completed. The rational behind worshipping the jewelry and cash is that it is believed that these are the forms of Goddess Laxmi (Laxmi is wealth). We pray to God to bless us and our near and dear ones with lot of happiness and wealth.