If you've just been listening to popular tunes, you're in for a gigantic new world of music.
Classical music shares a lot with popular music.
After all, in the 18 th Century it WAS popular music. People danced to it in kingly chambers and pianists had musical duals to determine who was a better musician. Today, pop artists lift melodies from classical music all the time. Think of it as a medium for a composer to express feelings. He uses rhythm, melody, and harmony to create whatever emotional worlds he desires.