Tanta is the right way of chanting mantras, the right movements to have when chanting mantras, the right body postures to have when chanting mantras. Each one of the poses in the tantra has a mantra attached to it. Lord Shiva himself developed this technique so as to move the energy in each chakra. In doing these poses and chanting the mantras, one can move energies so as to speed up the process of enlightenment.
Tantra has been misinterpreted by the humans and twisted into something sexual, but originally it was something divine given to us by lord Shiva.  It was given to us as a journey, however we tainted it by making something sexual of it. The first truth of tantra is that we could achieve godliness. It is still there, but the right concepts need to be understood. . On the other hand, nobody ever reached enlightenment through tantra.