Write an opening paragraph that introduces yourself and what the nature of your project is. Make the opening sentence an attention-grabber so the agent will want to read more. Be friendly and, if possible, appear knowledgeable about the type of material that suits the agent's taste.
Write a one-sentence "logline" of your project. The logline, sometimes called the one-sentence pitch, is what's used in Hollywood to quickly describe your project.
Write a synopsis of your story in 3 to 5 sentences. Hollywood movies are based on variations of the classic three-act structure so be sure to clearly explain the beginning, middle and end of your story.
Write a brief "bio" of yourself. List your relevant film experience, or education, that qualifies you as someone worthy of the movie business. If you have no experience or film related education, include any significant information that might help "sell" yourself. If you have one, offer a compelling reason why the agent would want to consider your project.
Write a brief closing paragraph. Be concise, yet thorough. You want to appear persistent without being overbearing. Above all you want to appear courteous, and honored that the agent would even take the time to consider your material.