There are several ways you could go on this, but my suspicion is that one will get you better results than the others.
I could tell you that art plays a large part in making our lives infinitely rich. Imagine, just for a minute, a world without art! (You may think “So what?”, but please consider the impact that lack of graphics would have on your favorite video game.) Art stimulates different parts of our brains to make us laugh or incite us to riot, with a whole gamut of emotions in between. Art gives us a way to be creative and express ourselves. For some people, art is the entire reason they get out of bed in the morning. You could say “Art is something that makes us more thoughtful and well-rounded humans.”
On the other hand, art is such a large part of our everyday lives, we hardly even stop to think about it. Look at the desk or table where you are, right this minute. Someone designed that. It is art. Your shoes are art. Your coffee cup is art. All functional design, well done, is art. So, you could say “Art is something that is both functional and (hopefully) aesthetically pleasing to our eyes.”
You might say “Art is in a constant state of change, so nobody can really pin down what it is.” The constant change part is true, but the not pinning it down part is going to get you a bad grade. It may even raise a comment or two about your being some sort of wisenheimer. Don’t go this route.
You might even say “Art is subjective, and means something different to every single person on earth.” This, too, is the truth. I would caution against this approach, however, as it would require a stack of paper from here to the moon to cite all of your 6.3 billion references.
Now, everything just stated has elements of truth, but is largely based on opinion. My opinion is, frankly, useless in your paper-writing endeavor. Form your own opinions (that should be the reason you are receiving an education, after all), and be sure to sprinkle them in your answer…which needs a factual basis, so here are the cold hard facts:
Art is form and content.
“Art is form and content” means: All art consists of these two things.
Form means (1) the elements of art, (2) the principles of design and (3) the actual, physical materials that the artist has used. Form, in this context, is concrete and fairly easily described – no matter which piece of art is under scrutiny.
Suppose you’ve written: “One half of all art is form. Here is how Goya’s The Shootings of May Third, 1808 fits in.” You would then go on to provide details about how Goya used color, value, space and line (elements of art). He used balance, contrast, emphasis and proportion (principles of design). He composed the aforementioned elements and principles on canvas, using brushes and oil paints (the physical part of “form”).
The example just given employed a work of Western art, and was written in English. It doesn’t take much of a leap in imagination, though, to understand that the concepts behind “form” could be applied to any piece of art, created anywhere on earth, at any time, using any language. With that, we have successfully covered “form”.
Content, now, gets a little more tricky. “Content” is idea-based and means (1) what the artist meant to portray, (2) what the artist actually did portray and (3) how we react, as individuals, to both the intended and actual messages.
Additionally, “content” includes ways in which a work was influenced – by religion, or politics, or society in general, or even the artist’s use of hallucinogenic substances – at the time it was created. All of these factors, together, make up the “content” side of art.
Returning to the Goya example, you might comment on the fact that the shootings were an actual event. Napoleon had invaded Spain, at the time, and subjected it to six years of war and revolution (political and social influences). There had been a revolt by citizens of Madrid, and they were summarily executed (historical context). Goya, obviously, didn’t think this was good and recorded the stark horror for all posterity. (He was successful at conveying that which he meant to convey.) We react to the painting in our different ways – usually with mixed feeling of revulsion, anger and sorrow.
Again, we are discussing “content” using one picture as an example, but the same parameters apply to any piece of art.
That’s my best reply, then. The first four paragraphs are applicable – with infinite variations, up to, and including, “The way my girlfriend puts on her eyeshadow is art.” Just be sure that your main argument includes “Art is form and content“. You can certainly think of some great examples using works of art that you know and/or enjoy. Now – go get cracking on that paper and, next time, don’t wait until the last minute.