Okay, so you know how when we want to learn how to do something like tying our shoes or drawing a picture, we ask someone who knows how to do it already? Well, the same thing goes for learning about how to be a good Muslim and following the teachings of Prophet Muhammad.
The things that the Prophet Muhammad said and did during his lifetime are written down and collected in books called hadith. Hadith studies is all about learning more about these books and looking at them really, really closely to understand what the teachings of the Prophet Muhammad were.
It's like being a detective - you have to investigate and ask questions to make sure that the information you're studying is accurate and can be trusted. Hadith scholars study the language and history of the time when the Prophet Muhammad was alive to make sure that what is written in the hadith books is true.
They also compare different hadith to make sure that they all say the same thing, and they look at the chains of people who passed down the hadith from the time of the Prophet Muhammad to the present day to make sure that the information hasn't been changed or lost along the way.
By studying hadith, they can learn more about how to live a good life as a Muslim and be more like the Prophet Muhammad.