How do you compare and contrast two different music covers?

In order to answer this question, it's important to first break down the elements of the music covers you want to compare/contrast--this will largely depend on what kinds of music covers you want to focus on. Let's use these as an example:
An acoustic guitar cover of Frozen's "Let it Go" versus an electric violin cover of "Requiem for a Dream" (see links).
If you compare/contrast these two items, you might focus on the following:
Compare: Both covers focus on melody.
Compare: Neither cover uses vocals.
Contrast: The violin cover is live, while the guitar cover is not.
Contrast: The violin cover is produced (multiple clips stitched together), while the guitar cover is not.
Contrast: The violin cover takes a classical modern approach, while the guitar takes a pop modern approach.
Of course, there are many other things you could talk about in a compare/contrast essay on this topic. You might focus on the sounds of the instruments, the expressions of the artists, the originality of the cover (is it a tight cover or is it interpretive?), the overall quality and expertise of the artists, the video format, and more.
Finally, I'll add that a compare/contrast essay on this topic should function like any other compare/contrast essay in formatting. You can choose either a line-by-line compare/contrast or a paragraph-by-paragraph format. In a line-by-line format, you can choose an item and talk about how both covers compare on that item. In a paragraph-by-paragraph format, you can use one paragraph to talk about one cover and the next paragraph to talk about the other.
Good luck!