For most of this era, music in Europe was the Church's domain. Monks sang plainchant — unaccompanied, single-line melodies — as an act of worship, not entertainment. The idea of music as art for its own sake barely existed.
What changed everything was notation. Once Guido D'Arezzo invented a system for writing pitch down on a staff, music could be taught, shared, and built upon. Polyphony — multiple voices singing different lines simultaneously — became possible. The "New Art" (Ars Nova) of the 14th century was the result: complex, rhythmically sophisticated music that the Church initially resisted and eventually embraced.
Alongside sacred music, secular song flourished in the courts of southern France (troubadours) and northern France (trouvères). These were the pop songs of their day — love songs, dance music, narrative ballads.