Scientists estimate that there are between 3 and 7 x 1022 stars in the universe, or between 30 and 70 billion trillion. This is actually a relatively small number by some standards. For instance, the number of atoms in the Earth is roughly 1050, and the number of atoms in Mt. Everest is about 1040. The number of atoms in half a kilogram of rock is roughly 1025. Avogadro's number, which represents the number of atoms in 12 grams of carbon, is about 6 x 1023.
The stars in the universe are aggregated into many layers of organization -- beginning with star clusters, which coalesce in galaxies, which are members of galaxy clusters, which are in turn members of superclusters, which are in turn members of super-superclusters, all the way up to the largest features in the universe, such as the Great Wall, a galactic supercluster which is about half a billion light-years long, a third of a billion light-years wide, and 15 million light-years thick. At its highest level of organization, the galactic clusters are distributed in "filaments and voids," thin filaments of galaxies separated by vast voids.
The typical unit of organization in the universe, the galaxy, contains anywhere between about 10 million and one trillion stars. Our Milky Way Galaxy contains between 200 and 400 billion stars, depending on the exact number of low-mass dim stars, which is highly uncertain. There are approximately 80 billion galaxies in the observable universe, a similar number to the number of stars in a galaxy. These galaxies are spread out across a universe that is at least 93 billion light-years in diameter, and perhaps much larger. 93 billion light-years is only the diameter of the universe that we can see -- the visible universe -- reaches of the universe beyond this are concealed by the cosmic microwave background radiation, a field that is created by the hot plasma that was omnipresent in the first 300,000 years after the Big Bang.
