In the traditions of yoga the teachings are divided into those `revealed` scriptures such as the Vedas and Upanishads; the vedas are said to have been revealed during a revealed during a golden age of humanity, and those secondary revealed teachings which it is suggested were to guide humankind through the dark age of `kali-yoga`.  The `kali-yuga`, Tantric-Puranic Age is said to date between about 500 – 1300 CE

The tantras, agamas and puranas all develop the vedic concepts of teaching into forms which are more `user-friendly` for humankind. Particular rituals, practices and philosophical concepts are described according to the basic beliefs of followers.  Thus there are differences between the north and south of India , between Shaivites, Vishnavites and Shaktism etc. 

A major recognition in the tantras is the place of the female, usually conceived of as Shakti, but also Kali, and Durga etc.  In rituals and practices there is a vast body of teaching incorporating the use of mantras, yantras etc.

One of the aspects of Tantra which attracts a lot of attention in the common mind, and is a good reason why it is said that the teachings of yoga should be kept secret from the idle, curious enquirer, is that of sex.  It is true that there are practices involving sexual intercourse between two people but the aims of these couplings are not to achieve a `Western` idea of orgasm, but to direct and utilise the orgasmic power of Shakti and Shiva; the combination of the powers of the male and female, to bring about the great release of Kundalini energy to experience the power of Samadhi, bliss.

One of the essential features of the teaching of yoga is that unlike the revealed teachings of Judeo-Christianity and and other prohet based faiths, it is open ended.  There is no reason why new teachings should not be accepted to lead humankind into the next stage of spiritual development.