Durga Saptashati is also known as Devi Mahatmyam. At a basic level it is a text celebrating Maa Durga's victory over multiple asuras that had been troubling humanity and the gods. On a deeper level, it is more than a text. Durga Saptashati includes four hymns to Devi, including Ya Devi Sarva Buthesu. It also has a deeper esoteric meaning for those focused on their own spiritual development.
Devi Mahatmyam can be recited throughout the year, but it is often recited during Navratri
You can search YouTube for other videos #DurgaSaptashati. The ones below are videos that I have enjoyed.
The text translated into English, with and introductory exposition, can be found on the Vedic Astrologer website.
This YouTube play list has an overview and the chants for each day. Durga Saptashati Chants
Durga Saptashati — The Esoteric Meaning
A Complete Overview of DurgaSaptashati - Stories, Symbolism & Sadhana Understanding the Dasha-Mahavidyas - with Shlokas from Tantric and Puranic Texts
Complete #DurgaSaptashati - 13 Adhyayas - Sanskrit Guided Chant