What is the origin of the universe?
The scientific consensus is that the universe started with what is called the Big Bang: an incredibly hot and dense primordial state. The Big Bang is inevitable given the cosmological standard model because of two things: we can observe that our universe is expanding today and that the universe contains too much mass for a scenario in which the universe would have contracted and then expanded again. Despite the name the Big Bang was not an explosion that happened somewhere. Instead it's simply the point in time at which all points in the universe were infinitely close together (at least in theory, there are likely parts we don't understand related to dark matter). Still, so far all experimental results in cosmology are consistent with the Big Bang. The history of the universe is very complex so the Big Bang alone cannot satisfy this your question about its origin. Do you have specific questions about the Big Bang nucleosynthesis, inflation, the cosmic microwave background, or the formation of stars and galaxies?