So, you've decided to indie publish. Good for you, but remember, some hard work lies ahead.
First, you must commit to being a detail person. You want the best version of your work out there for public consumption. Your author reputation is on the line.
Second, decide on the publishing platform you will use and become familiar with it. For instance, I found that if using Kindle Direct Publishing, my manuscript transferred easily if it was written in Word rather than in a Google doc.
Third, prepare the entire book document before you transfer it. This means preparing what is called the front and back matter as well. What do I mean by this? Pull some books off your bookshelf, and look at what is written on the pages before the story actually starts -- this is the front matter. There are blank pages, a copy right page, a dedication, extra title pages, sometimes a table of contents. If you want your book to appear professional, you need all these "extra" pages. These pages appear in a certain order. Model the appearance, type font, and order and your work will appear professionally published.
Look at the back matter in these books as well. Back matter is anything that comes after the book is finished. You'll need an "about the author" page. Read some professionally done examples and model yours after theirs. Will you need author notes? Look at several examples of what other authors do.
Then you'll need to finalize the actual text. This involves inserting either a heading or a footing for page numbers. Again, look at several professional examples and decide which basic design will work for you. Word offers you several options that can be tailored to fit your needs.
This is also the time to finalize other details. What font do you want the body of your text to appear in? Take out spaces between paragraphs, unless it is used as a device to indicate a change in setting. Make sure that paragraph indents are only about 3 spaces, not the typical 5. Don't indent the first paragraph of each chapter. (Don't believe me on this one? Check out some professionally published works!) Do you want an oversized letter at the start of each chapter? Play around with that. What font and size should your chapter headings be? Should they be centered? Flush to the right or left margin? Should they have titles? If they have titles, you'll definitely need that table of contents.
As you can see, there are a lot of decisions to be made and a lot of work to be done. Take your time, and do it right. Now is not the time to rush. Remember, you want your work to look its best out there in the world!