What is how does universe differ from a galaxy?
A galaxy is a collection of stars and the universe is the collection of galaxies.
Our Milky Way galaxy is just one galaxy, a large collection of gas and stars, among over 300 billion galaxies which are thought to exist in the known universe.
Our knowledge of the universe today is extremely limited due to its size and our ability to study and understand what we can see. Right now astronomers believe the universe is about 45 billion light years in size but they don't really know. We are only at the very beginning of our understanding of galaxies and the universe.