In Greek mythology, the original male sky god (Uranus) mates with the original female earth goddess (Gaia) and creates the generation of gods known as the Titans. A brother and sister among the Titans, Cronos and Rhea, mate and produce the generation known as the first six of the Olympian gods. A brother and sister among these six Olympians, Zeus and Rhea, mate and produce the rest of the Olympian gods.
With the shift toward transcendent monotheism during the Axial Age, there would be no role left for female goddesses, since there was no longer a pantheon of gods to be created, perhaps through several generations. The sole god (or two, in a dualistic religion like Zoroastrianism) had always existed, and will always exist. He does not need a story about who his mother and father gods were.
Like Christianity, Mormonism posits a variety of not-godly yet not-mortal beings, such as angels and demons. They are all of the same genus -- Heavenly Father's spirit children who have not yet been born on Earth. Reminder: Mormonism teaches that the soul of each mortal person came from a spirit being in the pre-mortal stage of existence.
Lucifer is one of these spirit children, although he was denied being born on Earth, for his rebellion. So is the pre-mortal spirit form of Jesus Christ, who before being born is called Jehovah in Mormonism (his, and our, Heavenly Father is called Elohim). Spirit children also include the demons, those pre-mortal spirits who sided with Lucifer and against Jehovah (pre-mortal Jesus) during the War in Heaven. And they include angels such as the archangel Michael.
Unlike Christianity, Mormonism does not hold this cast of spirit characters to be the production of the sole creator god. Instead, they all came from a physical marital union between the god Heavenly Father and his wife, the goddess Heavenly Mother. Reminder: gods in Mormonism have physical, flesh-and-bone bodies that are human in appearance, although in glorified form that is not subject to sinfulness, decay, death, and so on.
Given the emphasis that Mormonism places on the corporeal similarities between mortals and gods, the natural conclusion is that the act which created our world's spirit children resembled the act by which any mortal father and mother create mortal children. Yep, bumping their glorified uglies is how Heavenly Father and Heavenly Mother created our pre-mortal spirit forms.
This gives Mormon women quite a bit more to strive for than in other religions. Where else can they become a creator goddess in their own right? Recall that in Mormonism our ultimate goal is to reach the highest degree of "exaltation" and become creator gods ourselves, producing a race of spirit children, shaping their world, receiving their worship, and so on.
Men can expect to play the role of Heavenly Father, overseeing the shaping of the world and the creation of life and mankind. Women cannot expect those roles to play, but women are bored anyway by creating worlds out of Lego blocks, playing Sim City, and looking after an ant farm. Women can look forward to a role that truly matters to them: giving birth to the spirit children of her world, and nurturing them during their child-like pre-mortal spirit existence -- and without having to change diapers and breastfeed in the middle of the night!
Plus, women will be married to the head honcho god of their world -- not too shabby. Even better, that head honcho won't be just any old god, as though it were a Cinderella story. In fact, their godly husband will be the exalted form of the man to whom they were married during their mortal lives, continuing their Earthly marriage in exalted form for eternity.*
Because of the blatantly pagan nature of their Heavenly Mother goddess, Mormons try not to draw too much attention to her, as that might raise suspicion among the outsiders. They are instructed by their leaders not to pray to her or worship her, and to mention her as little as possible in church meetings and in lay discussions. And being inveterate rule-followers, they go along with it.
That's not to say that she receives no worship, however. The lyrics to an early Mormon hymn, "O My Father" (written by a woman), summarize their beliefs in the "eternal progression" from spirits to mortals to gods, organized around the theme of birth to loving parents, growing up away from them, and returning home to them in maturity.
In two separate verses it mentions Heavenly Mother in addition to Heavenly Father, making an argument from common sense that our creator god must have a creator goddess as his wife (a prime example of the Mormon aversion to mystery):
In the heav'ns are parents single?
No, the thought makes reason stare!
Truth is reason; truth eternal
Tells me I've a mother there.
When I leave this frail existence,
When I lay this mortal by,
Father, Mother, may I meet you
In your royal courts on high?
Because of the distinctly non-Christian nature of their theology and theogony (creation of gods), Mormons try not to draw too much attention by setting it to music and broadcasting the message to outsiders. To minimize suspicion, the world-renowned Mormon Tabernacle Choir mostly sings and records Christian standards, especially for Christmas. To end on, here is a rare exception of them singing "O My Father":
* The highest degree of exaltation requires that you be married and "sealed" to each other by a Mormon temple ceremony. This goes beyond a normal wedding, and is more of an initiation ritual, only this rite of passage is bringing in a couple rather than an individual.