There are MANY videos which where created to explain this within the BALG YouTube channel. I do not say this to be facetious but if people are going to deal with Ahriman in ANY way… then initiative and the desire to dig deep within self is VERY important.
However to give you a break, which honestly is deserved by many but not all, especially when the said people are new to magick, I will briefly answer this to give you an idea of the answer.
Ahriman is the Antithesis of the Sun, or Ahura Mazda to the Zarathustrian’s of Persia. He is the Black Sun. If Ahura Mazda’s light is responsible for chemical reactions which sustain this physical existence then Ahriman is responsible for AL-chemical reactions which are conducive to change and evilution.
Ahriman is a God. Not just according to me based on any bias as the author of BMoA. This is not a matter of calling modern demons ancient Gods out of preference… no matter how true this may be. Zarathustra stated this himself calling these forces the GODS of “bad decision”.
I would take some time to watch the many videos produced to help introduce BALG clients and magickians to this lore in an in depth way. Be well and may you be empowered upon your journey of becoming.