Jakub the best way to work this out is to think about how many stars there are in our galaxy (the Milky Way) and then work out how many galaxies there are overall. We can only guess this really as all the galaxies are different but there is about 10,000,000,000,00 stars in a galaxy, and maybe 10,000,000,000,000 galaxies overall. So that gives us about
10,000,000,000, 000,000,000,000,00 stars altogether! Some people used to think there was an infinite number of stars but we can prove there isn't because the sky is dark at night. If there were stars in every direction it would stay light at night.