Navratri Puja is dedicated to Mother Goddess Shakti, especially her Durga and Saraswati form, and is performed during the nine days of Navratri in September or October. Here is Navratri puja procedure in Tamil in pdf format. The puja is based on the guidelines given by Kamakoti mutt.
Link - Navratri Puja Procedure in Tamil pdf
The puja is performed for peace, prosperity and happiness in family. It is also done for success in business and new venture. The popular belief is that success in Kali Yuga depends on the blessings of Mother Goddess Durga and Goddess Saraswathi.
The puja can be performed on any day of Navratri.