The shAkta philosophy (ShAktaM) talks of ShivaM in place of the actionless substratum Brahman. Even if it is actionless, it is Cit, knowledge, says advaita. In place of this Cit, ShAktaM talks of Cit-Shakti or simply, Shakti.
The Brahman of advaita peacefully rests in itself. In ShAktaM, on the other hand, the peaceful ShivaM has the Shakti, power or energy, that manifests as knowledge potential (Cit-Shakti) and this manifestation is its play as the multiplicity of the universe.
In advaita there is no second. What appears as the universe is only an appearance created by MAyA. MAyA has no relationship with Brahman.
What it is, and how it came all this is inexplainable. That research is not necessary.
What is needed is how to get out of it and obtain the personal realisation of the basic Brahman behind. And hence the path of jnAna.