So, there is a kind of music called classical music. And one of the most popular types of classical music is called a sonata.
A sonata usually has three parts: the first part is called the exposition, where the main melody is introduced. The second part is called the development, where the melody is played around with and changed a little bit. The third part is called the recapitulation, where the main melody comes back again just like in the beginning.
One of the cool things about sonatas is that the music usually tells a story. Imagine you are reading a book where the first part sets up the characters and plot, the second part gets really exciting and suspenseful, and the third part resolves all the conflicts and brings the story to a satisfying ending. That's what it's like listening to a sonata!
So, in summary, a sonata is a type of classical music that has three parts - exposition, development, and recapitulation - and tells a story through its music.