Namaskar Mitra,Gurujana

I want to know that what is the difference between Devi Durga's Swaroopas?This question may be a confusing one so Pardon my ignorance.I mean to say that during Durga Puja or navratri we worship the 9 Devis Devi Sailputri to Devi .But in Ashtami in Durga puja we also worship goddess Chandi/Chamunda.This puja is called Sandhi puja,it is basically the moment where Ashtami and Navami coincide and this is the moment when Devi killed the Demons Shumbh-Nishubh and Raktbeej,if I am not wrong.

So,please enlighten me on Devi Chandi or Chamunda.Are both same or different I have been a Worshipper since I was 5 years old but I have not been able to understand the difference.Maybe I should read some scriptures.

Anyways great minds please explain this to me.

Dhanyabad