In general, when you are having a hard time writing 300 words about a subject, it suggests that you need to do more research or define your focus more clearly.
Moses, Man of the Mountain by Zora Neale Hurston is an effort to retell the story of the Biblical figure of Moses. Hurston assumes that Moses, as an Egyptian, was a member of an African culture, and thus has him think and speak in an odd mixture of the language of the 1611 British King James Bible and early twentieth century African-American dialect. The setting of the story is in Egypt at the time of Moses, sometime between 1500 BC and 1200 BC; scholars disagree about the precise dating an even historicity of Moses.
There are three ways you can approach the issue of the setting of the story, Biblical, archaeological, or textual. In other words, you can look at how the Bible describes the Egypt of Moses, how Hurston describes it, or examine archaeological sources to describe the historical reality behind the stories. Although the Mosaic books of the Bible provide no clear evidence of which Pharoah ruled at the time of the Exodus, the PBS website gives an excellent overview of how Egypt appeared during the New Kingdom, and you can describe the different elements of Egyptian art and architecture pictured there.
In your description, you can start with an overview of the geographical location of Egypt in North Africa on the shores of the Mediterranean sea. Next, you should describe the Nile river and surrounding desert, and the way Egyptian civilization and agriculture depending on the Nile. You might include a description of the main vegetation, crops, and domestic animals. You can also describe the system of government, and the importance of the pharaohs as absolute rulers and conclude by describe the monumental architecture.