If you're at school you can just logon and write a new post. If you're out of school, at home or on holiday you can add a post by email. You can also share a Google doc and I'll copy it here so more people can see it and comment.
I really like that you think about your story before you begin writing. Pre-writing is so important for writers because it helps gather your thoughts. Do you ever draw pictures or talk with a partner before you write?