You had a great idea for a book, and then you started typing.... 1,000.... no, 5,000.... no, 10,000.... wait... 50,000 words later it occurs to you to check your formatting. You panic for a second, then think am I doing this right?
Writers, don't worry too much about this. The words themselves are the most important thing. Formatting a document is relatively easy, and it is secondary to your masterpiece of ideas. That said, there are a few things you can do to make things easier when it comes time to submit/publish.
Use Microsoft Word. It's pretty universal.
Use a basic font in 12 point.
Don't do anything crazy with the margins.
Don't add a line space after every paragraph (just go to the next line).
Don't type in page numbers.
Use only one space between sentences. A simple "find and replace" can help if you've already used two spaces.
Put all of the book parts in one document. One exception is photos/images--best to keep those separate for now.
Now, when you are done with your manuscript and find an agent or publisher to work with, you'll need to check out their specifications on submissions. Each company should have its own, so pay attention to what they are looking for (single vs double spacing, file type, etc.). But hopefully, after following some simple ideas above, prepping your manuscript will be a breeze.