their origins

The Buddhism of Tibet in general is what the Buddha first taught in India to his Indian disciples. Later, after his teachings had flourished for a long time, they were then translated into Tibetan.
The Vinaya and the other teachings given directly by the Buddha were not written down until long after the Buddha had passed away. People had to know the Vinaya by heart and repeat it verbally. Later, since discrepancies appeared between differing versions, there was the need to have the Vinaya put down in writing.
The Mahayana teachings appeared in several areas at the appropriate times and began to flourish. After writing them down, the panditas wrote their commentaries and treatises. The Mahayana spread in India for a long time, and later the Tibetan lotsawas translated these teachings into Tibetan.
The tantras of Secret Mantra were written down as volumes of scriptures by the dakinis and given to yogis who had truly accomplished the yidam deity. Each of these accomplished yogis personally practiced these tantras and gradually propagated them by transmitting and explaining them to others.

Orgyen Tobgyal Rinpoche