Weather apps provide current weather conditions, detailed forecasts (temperature, precipitation, wind), and severe weather alerts by collecting data from sources like the National Weather Service. Users can access information on daily conditions, hourly predictions, and future trends, along with historical data in some apps. The accuracy of these forecasts varies by app, with some, like AccuWeather and The Weather Company, claiming superior accuracy, and it's important to understand how to interpret different metrics, such as the meaning of a "chance of rain".