This is a document that you begin now and work on over the next four years. It is a formal document and needs to be presented seriously. There are at least two benefits for you in creating this document:

The process of writing and revising your personal statement will help you think through your goals for the future.
This document can be used when you write essays for scholarships, etc.

Your personal statement should be written in first person, but other than that, there is really no exact right way to write it. The development of ideas and organization of this statement is up to you.

But what should you say? Your understanding of who you are and where you want to go will change over time. For now, here are some things you may want to consider including in your statement (in no particular order):

an anecdote about what motivates you
what you wanted to be as a child (if relevant)
your future educational goals (as 9th graders, it would be appropriate to describe what your high school education will look like)
your future work/career goals
your understanding of what it would take to achieve your goals
what kind of person you are that makes your choices right for you
what extra-curricular activities you are involved in and why they help you
what you think you can/will contribute to your community, local and/or global
what matters to you (issues, ideals, values, etc.)

Your personal statement needs to be succinct, no longer than 500 words. Be precise in your word choice and careful in your organization. Have your cyberpartner or web pal (if you have one) read it and give you some feedback.