Yeah... really, it is necessary to do something before writing that first sentence. Before writing an essay, you need an idea.
In school, we write essays because we have to, but in real life we write essays because we are struck suddenly with inspiration.
You do not need to know the first sentence. Instead, think of ANY sentence. Write a sentence that tells what comes to mind when you look at the essay prompt. What is the prompt for the essay?
Welcome to essayforum, Garbriel!