Creationists believe the universe was created during seven literal days. While many do believe this, it’s pretty easy to understand it doesn’t mean a literal seven days. If Moses wrote Genesis, God would have to explain creation in terms that wouldn’t confuse the hell out of him or anyone else. Of course God could not explain the process of fusion, which is the life of a star, and the elements it involves, so he just said and let there be light. Nor could he explain the sense of the billions of years it took to mold the universe as it was. It would be baffling to comprehend back then. If you want to learn about creation from the Bible in more scientific and literal terms, I would recommend, just out of pure curiosity with no religious motive, to read some of the chapters of the book of Job, in which he marvels at creation much like you do.