How do I write a descriptive essay on my first concert?

To write a descriptive essay, you will want to focus on the five senses of sight, sound, touch, taste, and smell. You probably won't be able to do much with taste, but you will want to describe in detail the setting of the concert: how it looks, what sounds you hear, what the smells are, and the feel of it—for example, it is hot or cold in the room? What does the chair feel like? Are you playing an instrument?
As you describe the scene, you need to focus on concrete details. You don't want to simply say the concert hall was beautiful (if it was). You also need to describe the details that made it beautiful—such as the lights or the curtains on the stage—and to try to create a picture for your readers to imagine in their mind's eye. Be sure to include colors, for example, and anything unusual that might not be in a normal concert hall.
You can organize the essay by devoting one paragraph to describing what you see, one to sounds you hear, one to smells, and so on. Another strategy is to pretend you are filming the scene and then to describe what the camera would be capturing, adding in other senses as well.