How does CreateSpace deduct their cut of a print book?

They set a minimum price for the book, based on what it costs them to print it. You can set the retail price to anything above that. Whenever someone buys a copy, you get the difference between your price and the minimum, and CreateSpace keeps the rest. Depending on which channels you select for distribution (Amazon in the US, Amazon in Europe, various bricks and mortar bookshops), the minimum price might go up. That increase represents those channels' profits.

CreateSpace is a print-on-demand company, which means they don't print any copies of your book until somebody orders one (or more), and no money changes hands until that point. If a reader orders a copy, CreateSpace prints it, ships it, takes the money and gives you your share. You can order copies yourself if you want to give them to friends and family or sell them face-to-face. If you do that, you can buy them at cost - the minimum price, not the price you set for other people.

There's a little calculator somewhere on the CreateSpace site, where you can play with the factors that affect the price to see how much your book might cost.

What does you contract say?