About 3,000 stars are visible to the unaided eye on a clear moonless night. About 100,000 stars can be seen using a small telescope. There are an estimated one hundred billion (100,000,000,000) stars in our own Milky Way galaxy, although some estimates range up to four times that many, much depending on the number of brown dwarfs and other very dim stars.
A typical galaxy may contain anywhere between about ten million and one trillion stars. Therefore, using a very rough estimate of a hundred billion galaxies in the observable universe, and the number of stars in our own galaxy as a reasonable average, there may be around ten billion trillion (10,000,000,000,000,000,000,000 or 1022) stars in the observable universe, or quite possibly anywhere up to 1024.