If one has realized that mind is not a passive receptacle but a creative instrument, then one would know that a mytho-poetic looking onto self and world would, in some measure reveal (or, re-veil) self and world, as they have been envisioned. To engage this praxis towards Moksha (liberation) is to practise Tantra.
And to what measure does envisioning, create? The concept of "tapas" is helpful here. Tapas is one's reservoir of what may be called creative/spiritual energy. The greater the tapas, the more one "knows", rather than merely "believes". With enough tapas, "imagining" becomes too weak a word for what is then more fittingly called "a fervent envisioning". The ability to put forth this amount of effort varies from person to person. Patanjali makes the following simple yet profound statements: "That is called effort which produces results.", and "The Yogin possessing great intensity quickly moves forward in Yoga." Some things must be engaged in order to be understood. A stand-offish approach does not produce results here. One must decide upon an auspicious course and then put forth the effort required to produce results. Though Patanjali does not speak on Tantra, his words can nonetheless be helpful in learning how to engage oneself in Tantra-Yoga, and indeed in any endeavor whatsoever.
Now, how to decide upon an auspicious course? No matter what your Yoga praxis, it is crucial to behold clearly the goal. And the goal of Yoga, whatever praxis it might be, is Moksha, to attain/become what Buddha calls "the unborn, the uncreated, the deathless".
STILL MIND OR MOVING MIND
Two ways towards this: Still mind or Moving mind. Classical Yoga teaches the former method, while Tantra-Yoga teaches the latter. Classical Yoga teaches that the Yogin should wholly identify with the ultra-subjective pole of the subject-object duality. Tantra-Yoga engages the object, engages the vrittis (fluctuations), better known as the inner and outer worlds in all their guts and glory. And this engagement is artful, is creative; the vrittis themselves becoming a sort of launch pad towards the goal. Needless to say, this can be a rather colourful way to engage the process towards Moksha, especially when compared with Classical Yoga. Classical Yoga is the conscious, and exclusive engagement of the process towards the "absolute". Tantra-Yoga certainly does engage that very same process, but also artfully engages the relative. So, both directions are engaged simultaneously. Tantra-Yoga certainly does not exclusively engage the process towards the relative, for that would be to fall into "unknowing".
DUAL AND NONDUAL
Why not simply stop the mental fluctuations (vrittis) as Classical Yoga suggests and be done with it? Some feel that this is too one-sided an approach, that it devalues the material aspect of reality, devalues body and mind, relegates them all to an illusory status. It is reasoned that, if reality is whole, then its relative aspect must, in some sense be the same as the absolute. So, the attainment is right here, right now, in whatever form or stage one finds themselves in. The creative task then becomes the fruitful utilization of whatever is at one's disposal as an instrument towards Moksha; body, mind, material objects, one's station in life... whatever. The relative is not shunned in favour of the absolute; rather, the relative is envisioned as an "aspect" of the absolute, so is just as "sacred" as the abstracted absolute. So it is all One, the relative and the absolute, "Samsara" and "Nirvana", "Form" and "Emptiness". There is no real duality. Non-duality, or the essential sameness of the relative and the absolute is acclaimed. However, some dualists see danger, and sometimes an outright mistake in non-dualism, while some non-dualists see an unnecessary dryness, or an outright error in dualism.
Some have pointed out that Tantra-Yoga is potentially dangerous, can more easily entrap an individual within names and forms, rather than deliver to the "Formless". They say, playing with Vrittis is a fool's game, is like playing with fire. So there are two schools of thought, the dualistic and the non-dualistic -- Classical Yoga and Tantra Yoga. However, they need not be seen in strict opposition to eachother, each the other's antithesis. It is possible to see them as complementary, each fitting an individual at a certain stage of their unfoldment towards Moksha.
Classical Yoga offers a very simple, very direct praxis towards Moksha. Become absolutely still, right now, right here, and wait until the process thus engaged completes itself towards Moksha. Personally, I find that engaging the praxis of Classical Yoga enables me to concurrently engage the path of Tantra-Yoga with more safety and confidence.
To the extent that one has seen through the delusory belief of a wholly independent, objective reality "out there", to that extent one can safely play within it. So we are back to the initial statement: "If one has realized that mind is not a passive receptacle but a creative instrument, then one would know that a mytho-poetic looking onto self and world would, in some measure reveal (or, re-veil) self and world, as they have been envisioned." Please note that part of the phrase is "looking onto self and world", and not merely looking onto the world.
Even the experience of self unfolds within awareness, and because of this realization it can be said that self itself is "empty"; Buddha designates this as "Anatta" -- no atman/self/soul. The belief in an independently existing self, however it might be experienced or understood, is in the final analysis, something to be let go of too. So, there is play in Tantra, but the question need also be asked: "Who plays, what self plays?" Why is this important, why is it so? Well, its just that in letting this last bit go, there is revealed something which cannot be communicated, but is of a self-evident ultimate importance. This is not a matter of theory or metaphysical speculation, but experience. The only way to find out for yourself is to meditate, and while doing so let go of the idea of an independently existing self, and see. Though Buddha was quite emphatic about this, he also discouraged mere belief, even of his own statements, instead exhorting others to "see for themselves".