First it is usually agreed that music is sound. But how does it differ from noise or random sounds? We then usually agree that music is sound that is intentionally organized using various elements. The most apparent of those elements are melody, harmony and rhythm. A more elusive element to discern is form, and it is present in all music.
Music occurs in time, so the beginning and ending moments provide the overall framework. At the very least the music will have a beginning and an end. Some music is what we call "through-composed" without having sections that repeat. It simply will begin at one moment in time, and end at another.
But most music that we hear consists of sections that repeat mixed with sections of contrast. It's common to label each section with a letter to indicate the form. Some common forms are: ABA, AABA, ABACADA (etc.), AB (or verse-chorus). And there can be smaller forms within the overall form. And within the forms and subforms are melodies, harmonies and rhythms that repeat and vary, further adding structure to the music.
Melody, harmony, rhythm and form. As you listen to music try to become aware of and identify its formal structure. What are the sections that repeat? What are the sections that are varied? You'll find it in music from pop songs to symphonies.
A note from artist Helen Miranda Wilson: "You know that tune 'Honeysuckle Rose'? It came on the radio while I was making that painting. Plus the honeysuckle was blooming in the back yard. Its scent was wafting through the window. Repetition and variation: it's all I do, for years now. It's what breathing is."