(Note: This walkthrough will be done in Word 2007 only. If you have another version, you may be able to find the corresponding menus and still follow these steps.)
1. Go here to see a list of page sizes available for CreateSpace and choose one. (You might want to take a ruler and see how these compare with the books on your shelf.)
2. Open your Word Document and save it as [Title] - Formatted or whatever you wish. (Always keep this document separate from your manuscript.)
Your page should look like this:
3. Open the "Page Layout" menu.
4. Under "Size", select "More Paper Sizes".
5. Enter your desired paper size, chosen from the list back in step 1. (My Australian system defaults to cm, so I just type in "[x] in" and the system automatically changes the length (in) to the cm equivalent.)
I've chosen the 5x8 inches option.
It should now look like this:
1. Go here and read the useful information about margins. From the table on the right of that page, select the best margin for your book. (Since my book is more than 151 pages and less than 400, I'll be using ".75 in" margins all around, just to keep it simple.)
2. Select "Page Layout" > "Margins" > "Custom Margins"
If later on you find you don't like how the margins look with the text, you can change them. Try to keep within Amazon's specifications, though.
The next post will involve front matter and section breaks.