Playing a free story is a great way to evaluate the story yourself. If you want to send the story to someone else, though, you should click the Cancel button and use Add Cart to add the story to your account. It'll still be free, but will take you to where you can send the story as a gift to someone else.
Note that playing a free story this way means none of your progress is saved. If you close or refresh the browser, your progress will be lost. If you want your progress to be saved, click the Cancel button and use Add Cart to add the story to your account.
If you're fine not having your progress saved, click Play to get started. Enjoy!