The story of the birth of Kartikeya is explained here. Lord Kartikeya is also known as Skanda, Shanmukha, Subramanya Swamy, Dandayudhapani, Lord Murugan, etc…
The story of the birth of Kartikeya is mentioned in the Shiva Purana…. The story goes like this…
As Lord Shiva and Goddess Parvati moved on from Himavanth’s Palace to Kailash and were enjoying conjugal happiness, all the Devas, Brahma and Vishnu were all disturbed by the peak- evil activities of Tarakasura and the very purpose the wedding of Siva and Bhavani appeared to take a back seat.
A Divine Delegation headed by Vishnu sought permission to meet Siva to explain the grim situation and in a hurry to meet the Delegation spilt His Virya on ground and Agni Deva transformed as a pigeon pecked up the drops and could not bear the inflammation. Maha Deva Himself advised the pigeon to inject the drops into a woman of immense virtue.
Agni identified Six Women of Great Virtue and injected them into the pores of hairs on their bodies. They too could not bear the extreme effervescence and as directed by Himalaya relocated it into the violent flow of Ganges which carried to the bushes of reed (Sarkanda) and there appeared a Boy of mysterious radiance. Even while this sequence of events was happening, Devi Parvati was extremely furious that Her privacy was disturbed and worse still Bhagavan’s Virya was being wasted and in that fit of anger cursed the wives of Devas who accompanied their husbands in the delegation to become barren!
The birth of Kartikeya on the Lunar Calendar of the Sixth Day of the bright fortnight of Margasira Month (Krittika Nakshatra of Shashthi Tidhi of Suddha Paksha of Margasirsha Masa) brought the greatest joy to Devi Parvati and Maha Deva, unbelievable relief and sense of liberation to all Devas, and a feeling of frustration and apprehension of the Demons and followers of Takasura. Sage Visvamitra appeared at the spot and named Him as Guha, bestowed the Totality of Vedic Knowledge, endowed Him with the Title of Brahmarshi and blessed Him to lead Indra and Devas. Agni Deva gifted Him a Divine weapon ‘Shakti’.
Six Goddesses arrived at the scene and all of them tried to feed breast milk but the miracle Boy solved the problem of assuming Six Heads and mouths. He was thus known as Shanmukha. As He grew a year or two, He became restless and moved on to Krouncha Mountain and demonstrated His valour by crumbling it ; innumerable Demons got shaken and killed. Indra tested His valour by fighting it out with the former’s ‘Vajraudha’; Indra hit on Kartikeya’s left, right and central portions and out came three powerul entities viz. Shakh, Visakha and Naegam.
In the meantime, Sivaganas located Kartikeya and brought Him to Bhagavan and Parvati, who knew no bounds of elation that He was finally home. Kartikeya was crowned as the King of Kailashpuri and various Deities gifted away their weapons and powers and was declared as the Senapati – Commander in Chief. Now was the time that Tarakasura was destined to be destroyed; the Deities including Brahma and Vishnu could not with stand the fury of the Demon.
Finally, Tarakasura was challenged by Kartikeya, the Demon ridiculed Devas and said that they were seeking to keep a mere boy as a shield and fight behind him. But the ‘wizard boy’ attacked the huge ‘Asura’ with warm-up weapons initially and ultimately at an opportune time when the Demon was caught unawares applied the Shakti weapon deftly and hit on the Demon’s chest even as the biggest menace on earth at the time breathed his last instantaneously.
Kartikeya continued His battle escapades further on by hitting Banasura as the target from Kailasa Mountain to Kraucha Mountain as a simple feat and recalling the weapon Shakti back therafter. He set up three Siva Lingas at the Krouncha by His mystic vision viz. Kumareshwar, Pratigyeshwar and Kapileswar to please His father Bhagavan Siva. Yet another time, when a DemonPralamb tried to create obstacles to Devas, especially Brihaspati and Seshanag’s son Kumud who took refuge from Himself, Kartikeya repeated the miracle of destroying the Demon without even facing him.