The number of stars indicates the standard and amenities that you can expect in a hotel. The more, the more luxurious the conditions are.
However, there is no international document regulating the requirements that must be met in the facility to receive a certain number of stars. There are separate rules and scales in each country. In addition, there are also areas where such a classification is not applicable at all (for e.g. Scandinavia) or is voluntary (for e.g. England, France).
Therefore, these markings should be treated with distance and when selecting a hotel make sure each time to check what services are included in the price.