Lakshmi puja is a Hindu ritual performed during Diwali, the festival of lights. According to tradition people would put small oil lamps outside their homes on Diwali and hope Lakshmi will come to bless them.
Goddess Lakshmi is worshipped by those who wish to acquire or to preserve wealth. It is believed that Lakshmi (wealth) goes only to those houses which are clean and where the people are hardworking. She does not visit the places which are unclean/dirty or where the people are lazy.
In the Sri Vaishnava philosophy however, Sri (Lakshmi) is honoured as the "Iswarigm sarva bhootanam" i.e. the Supreme goddess and not just the goddess of wealth. This is an important distinction between Sri Vaishnavism and other materialistic philosophies.
Read more about Lakshmi Puja: **The Auspicious Moment**, Rite of A Diwali Puja