HI there @karolinak98 and welcome to the Community! 🙂 The heart function is visible in your radio/daily mix listening. This feature allows the station to determine which songs and artists you love so it will keep playing it in that station/mix. It will also automatically add it to Your Library (you can find these songs in the section called Songs). You also have the option to add it to a playlist once you click the heart. I attached a screenshot of what this looks like on the mobile app.