You will be asked for the number of words, because the size of the excerpt you want to use is crucial for the pricing of a permission. If you are not quite sure how many words you want to use, or you don't want to count, try to be as specific as possible. The rule of thumb is that 400 words is approximately one page. So if you want to use two pages of text, enter 800 words, if you want to use three pages of text, enter 1200, and so on.