The nine days and nights of Navratras mark nine different aspects of Shakti — Shailputri, Brahmcharini, Chandraghanta, Kushmanda, Skandmata, Katyayani, Kaal-ratri, Mahagauri, Siddhidatri and Aparajita. Shakti is that creates, preserves and also destroys. For a beginner, these may be broadly understood as triple forces of Durga, Lakshmi and Saraswati. The nine devis originate from these three devis which, in turn, have their origin in Adi Shakti.
The first three days are dedicated to Devi Durga. She is the devi of spiritual evolution and governs the transformation of universe, also called Yogmaya. She is the consort of Lord Shiv. In the human body, she corresponds to the tamas guna and region from chest to head.
The next three days are dedicated to Devi Lakshmi. She governs and preserves physical creation and its various aspects, also called Maya. She is the consort of Lord Vishnu. In human body, she corresponds to the rajas guna and region between navel and chest. In these days, sadhak stops intake of anna to keep the body light. Havan for Maa Lakshmi is done at the two sandhyas by making offering of a sweet along with ghrit.
The last three days are dedicated to Devi Saraswati. From her emanates gyan and all forms of arts, she is the devi of creation, also called Mahamaya. On the 10th day, Maa Durga or Maa Kali is invoked as on this day Lord Ram defeated Ravan.