Start with an outline. Or a list. List the things you've done (your experience) and your talents in the area.
Your outline may go something like this:
Paragraph 1: Introduction. Introduce yourself and give some of your personal information and background.
Paragraph 2-?: This is where your list can come in. For the things you've done and your talents which would be relevant, make each of those into a separate paragraph.
Final paragraph: Sum up why you want into the program and why you should be one of those six people who are accepted.
Be upbeat, confident, and bring across how much of a hard worker you are. Don't be cocky, but confident. And even if you don't have much experience, stress your strong points and what would make you valuable to that program.
Hope that helps a bit.