Tantra is not something you can learn from a book, because that would be a copy of someone else’s tantra. You have to invent your own. Then quickly grab that tantric knowledge, and move swiftly on. Lifes too short. And there lies the great secret of tantra.
It has to be something that comes from within yourself. If you want to know anything about tantra by all means have a look on the internet to see what others have to say, but the answer for you, will come when you find a quite space, lie down and breathe deeply and Hum, OM(pronounced AUM).
Place one hand on your heart and the other on your cock and let them vibrate. When you feel a connection ask yourself the question, and the answer will just cumm.