Here are the basic parts of a business plan: 
Executive Summary: Explain exactly what you're doing an why, then give an overview of what you're going to cover in your plan. 
Target Market: Who are your customers? 
Competition: Who is your competition? Don't just focus on other companies with the same product or service, but also companies who are targeting the same audience as you. For instance, People magazine's editors might see Entertainment Weekly as competition, but they are also competing with TV and movies for your hard-earned cash. 
Marketing Strategy: How do you plan to get the message of your product to your target market?
Operations Strategy: How will you operate? Who will do what? How will you get your products assembled, packaged, and distributed? Who will be in charge?
Financing Strategy: Just like it sounds – how will you pay for your business? How will you pay for advertising? Will you apply for loans or investors? When do you see your business as becoming profitable?
Use of Funds: How do you plan to use the money you receive through your business plan?

This is just a brief explanation, and you can always include more in your business plan than we have here. In most cases, though, don't use any fewer sections than we have here.