Lakshmi Puja occurs on the fourth day of Deepavali and involves the worship of Maha Lakshmi. Maha Lakshmi is the goddess of wealth and prosperity, bestowing these abundantly upon her devotees. On Deepavali she is prayed to for prosperity and her blessings. Prayers to her are for all four aspects of life, Dharma, Artha, Kama, and Moksha. In other words, they ask for both spiritual and material wealth.
The day typically begins with a bang of fire crackers and ends with the performance of Lakshmi puja in the evenings. To indicate Her long-awaited arrival, small footprints are drawn with rice flour and vermillion powder all over the house. Entrances are decorated with lovely, colorful motifs of rangoli to welcome the Goddess or Wealth and prosperity. Lamps are kept burning all through the nights and women make it a point to purchase some gold or silver, or at least one or two new utensils, as it is considered auspicious and a symbol of prosperity, a manifestation of the goddess Herself. In South India, cows are offered special veneration and are adorned and worshiped as the incarnation of Goddess Lakshmi.
She is typically portrayed wearing red. Red represents the color of action and she is the Deity of prosperity. In the Bhagavad-Gita, Lord Krishna discusses Karma Yoga which is fundamentally about doing your karma (duty) in mood of service to the Lord.