In the past few years, we have covered plenty of astronomy apps that can enhance your stargazing experience. The Astronomy Star Type Calculator app can teach you more about the stars. You can use this app to learn about different classes of stars from M to O. Simply enter a surface temperature, and the app does the rest.
You simply have to enter a surface temperature 250k to 60,000k to learn about each star class. Example photos for stars of each spectral class are also available.