Describing something, whether it is a text or an object or an experience, is a way of bringing the subject to life in writing through carefully chosen details and language. When you are asked to describe something, you are usually being asked to portray it in a way that depicts your understanding of it rather than just your ability to re-tell it.
Because description is not about retelling, you don’t need to describe every detail and element of the subject. Think of choosing the details of your written description in the same way you would choose how to describe someone you know to stranger. What is most important about this subject? What characteristics or details stand out to make this what it is?