Diwali is a five day festival celebrated in the Kartik month according to Hindu calendar. .
Dhanteras is celebrated on the 13th day. That is the day that Kuber was returned his treasure by Rama after defeating Ravan. That is the day that traditionally new clothes, sweets, Gold and Silver, Diyas and Puja idols are bought.
Narkachaudasa in celebrated the next day. That day Krishna with the help of Satyabhama (Lakshmi's avataar) killed Narakasura. On this day the homes are cleaned, trash taken out nad old things given away (Basically the Narak from homes is gotten rid off)
On Amavasya, Diwali is celebrated. That is the day Ram returned to Ayodhya after 14 years of Vanavas. According to Valmiki Ramayan that is also the day that Ram brough Sita home after their marriage. On both the occasions Lakshmi in the form of Sita entered the house and that is why we worship Lakshmi. According to some legends that is also the day that Lakshmi appeared from the sea after Samudra Manthan.
The next day is Govardhan Puja. That day Krishna picked up Mount Govardhan on his little finger to say Brindavan village from the wrath of Indra.
The fifth day is Bhai Duj.