im 13 and how do i write a book?

[Shaun]

First, plan your story.
Write it on a word processing document (such as Microsoft Word/Kingsoft Writer/LibreOffice Writer), keep in mind that it may take up to a year to complete writing your story
Check your story to make sure that it is perfect (in some cases, there may be a small amount of errors, it doesn't really matter because I even saw typographical errors happening in books that has already been published)
Convert it to PDF.

Then you will have to find a publisher, upload your pdf file to their website, and send them a quote, they will print the document you uploaded, and bind it into a book for you.