One of my favorite days when I'm teaching a music theory class is when I ask my students to define "music". How do we pare music down to its essence and find a common definition that we can agree upon and that will apply to any style? What a challenge! 
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. 
Happy listening!

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."

As a musical performer I've always been intrigued by musical styles and the challenge of authentically playing in a given style. What makes classical music sound classical, rock sound rock, etc.? 
Style implies uniformity, an overall set of rules or standards. Then, within those sets of rules, it's the subtle differences, the rearranging of order, the little twists and turns that a particular composer or performer takes that make each piece in that style unique and interesting. Repetition and variation.
A criticism sometimes levied at an unfamiliar or disliked style of music is that "It all sounds the same". Well, in fact, it does. That's what a style is supposed to do - repeat itself. But once we are familiar with the individual pieces within a style we can become immersed in the unique subtleties of each piece or performance and focus on the variations. The repetition provides form and familiarity while the variation provides interest.
For a non-musical example, when I toured Korea with the Rhode Island Saxophone Quartet it took me about three days before I stopped getting the names of our Korean hosts wrong. There was a uniformity to their appearance that at first struck me as "all the same". When I was finally able to perceive the uniqueness and subtle differences of each person in the group I no longer got their names mixed up.
For a musical example, cool jazz and hip hop are often perceived as very relaxed and laid back styles. They definitely have that vibe to them, but they are very precisely relaxed and laid back. There are very specific things that the musician must do to achieve that feeling. A style of rock music might be described as "driving"; something classical might be "expansive". How is all that achieved? 
To perform as authentically as possible in a given style I need to discover the uniform characteristics of the style as well as the subtleties of the differences. Repetition and variation.