The creation of the Solar Bodies is a subject-matter related to Maithuna, Sexual Magic, without spilling the semen, and it is performed in the flaming forge of Vulcan, in the Ninth Sphere (sex).

This is a work bitterer than bile; daily sexual connection of the same man with the same woman, over twenty or thirty years, without ever spilling even a single drop of semen, without allowing the semen to leave our organism. - Light from Darkness

This whole book addresses your question.

Simply stated, the second birth is a work of the Divine Mother that she facilitates when we provide the raw elements. The Kundalini is her energy; she uses that to create those bodies, and later, to liberate her child (the soul) from the ego. We ourselves cannot do these things; we ourselves do not have the powers that she has.