Writers, especially students, often sit down with an assignment and expect to start writing at the first word. This is very difficult to do, and the writer often becomes discouraged and decides that he is just not able to do this. This is not true, of course. All of us are more than adequate users of our native languages or we would not be able to survive in the world. We talk to our friends without being stalled in this way, so it must be something else that is getting in the way of getting this piece of writing launched.
That “something else” is a failure to plan―to do the preliminary tasks necessary to generate that first word, that first paragraph, and the remainder of the essay. You must have knowledge about your topic before you can make decisions about what you want to say about it and how you want to present your material.