When writing a description, you need to think about the advantages a piece of descriptive writing has over a photograph. Descriptive writing lets you influence your reader and give them a strong bias against or for the place you are describing. This is what creating at atmosphere is.
When you look at your picture you've been asked to base your description on, think about what emotion you want to pass on to your reader. Is your location a joyous one? Is your location a scary, intimidating one? What language/phrases would be best suited to making your reader feel that?
Compare the two sentences below that are being used to describe a park in the winter:
What are the two types of atmosphere (emotions) being created?