Writing A Book?
I work with a number of people who are writing: murder mysteries, biographies, autobiographies, how-to books, magazine articles. I’m in awe; manuscripts are everywhere!
Perhaps you are writing (well, typing) too.
My suggestion: concentrate on typing (including correct spelling and punctuation!), not formatting.
I have seen writers preoccupied with tweaking fonts and type sizes, adjusting margins, contemplating left vs full justification, and bolding and un-bolding chapter headings. The fact is that the choices you make may not matter; they may not be up to you.
What does matter is who might be printing your manuscript when it’s finished. If you have a publisher, have contracted with a company to print your work, or are uploading your book to Amazon for sale as an eBook, check with them. They will tell you how to format your document, and then they will apply their standards to it.
Unless you are printing your book out of your printer — in which case you will need to make formatting decisions — focus on the content.
There are plenty of people who can format your work, many fewer who can write it.