Can I use the word processing program that came with my Mac?

Sure. It’s just sort of a Word Lite product. In the end, assuming your book is straight text, you’ll want to save your manuscript as a Word doc file or as a PDF file before submission. And remember, no extra lines, no extra spaces after periods and no tabs for indenting.┬áIf you’re using CreateSpace, download their formatted template and conform your manuscript to its requirements. Keep it simple and you should be fine. If you paint yourself into a corner, hire someone to help with your formatting. Don’t let this process get in the way of writing and getting it done.