What does MP3 converter do?

What does an MP3 converter precisely accomplish? Is it some sort of a magical device that transforms your favorite songs from one format to another, allowing you to enjoy them seamlessly across different devices? Or is it more complex than that, with hidden functionalities that only the tech-savvy can appreciate? And how does this process work, exactly? Does it require any special software or hardware, or can it be done with ease, right at your fingertips? Share your insights, if you please.