Brahma creates the world, Visnu sustains it and Siva destroys it. This process of creation (srsti), preservation (sthiti) and destruction (pralaya) perpetually continues in that cyclic order.
If the world were a myth as some extreme forms of Advaita Vedanta philosophy aver, there would have been no theology and hence no theological problems. But the world being a fact of our day-to-day experience, cannot be explained away or wished away! Once we accept it as real-whatever may be the degree of reality we ascribe to it-the theological questions of creations and creator will have to be squarely faced and answered. This is what the various Hindu scriptures have attempted.

Three types of tendencies or characteristics seem to accrue to every created object. These have been technically designated as Gunas: Sattvaguna, Rajoguna and Tamoguna. These three Gunas in their purest form, are fundamental entities, the permutation and combination of which produce this world of phenomena. Of these, the Sattvaguna makes for light and lightness, goodness and purity, knowledge and wisdom. It can be likened to the centripetal force. Tamoguna, which is the antithesis of Sattvaguna, is responsible for all that is dark and heavy, evil and impure, ignorant and deluded. It is the centrifugal force as it were. It is the business of Rajoguna to maintain a delicate balance between these two opposing forces. Hence it has got to be in a state of constant internal tension and activity. This restless activity is its chief characteristic and it manifests itself as passion and ambition in the psychological world.
The three deities of the Trinity, correspond to the three Gunas in the cosmic play of creation, preservation and destruction. Visnu represents Sattva, the power of existence and preservation. Siva represents Tamas, the power of annihilation. Brahma stands in between these two and represents Rajas. He symbolises the possibility of existence resulting from the union of opposites.