In Big Bang, 13.7 billion years ago, the universe was created.
Scientists don't know what happened before that. But it's possible that our universe is one out of many others (the multiverse theory), and the Big Bang occured due to an earlier universe collapsing.
Religions explain it by saying their god created Big Bang.
Consider psychology, the principle of self fulfilling prophecy" If you believe a thing to be true, then it becomes true for you.
Science cannot prove or disprove when and how the Universe was created. Investigations and scientific philosophy point to an initial event, called the Big Bang.
Hinduism gives some flexibility; Hinduism also teaches, if you believe a thing to be true, then it is true for you. Yad bhavati, tad bhavatum, as the feeling, so the result. So if you feel that the Universe was created from the vibration OM, the pranava, the basic act of creation, then that is true. If you believe the universe was created by the Big Bang, then that is true for you. Arguments on the matter do not prove anything one way or another, nor do they prove or disprove the existence of God.
It was said above, the Big Bang occured due to an earlier universe collapsing. Hinduism teaches that Universes are born and die, and there are universal cycles of existence on larger scales. These are called "Days of Brahma".