Perspective is a Free App for the iPad. You can use it to play many available free stories. To play a premium story you may have to make a nominal in-app purchase. You will never be charged without explicitly agreeing to the purchase via standard ways.
You may also create stories to experiment with the authoring features. There are many types of scenes that are available for free that you can add to your stories. Some premium scenes like the motion charts are available for purchase at a nominal cost. These are one-time purchases that let you use those scenes in any stories you create.
If you have purchased the Authoring Kit using an older version of the App, you already have access to all the premium scenes. You do not have to purchase them again.
Alternatively you may purchase a Pro Subscription that gives you access to all scene types and other premium features like the ability to export and publish your stories.
You may want to publish stories you have authored so as to share them with others. To publish a story, select it on the home screen and tap the 'PUBLISH' button. You will have to provide some basic information and agree to the publishing agreements. Initially, you are limited to one story in your published stories bucket. However, you can expand this to 20 stories by purchasing a Pro Subscription. An option to purchase this subscription is presented to you when you attempt to publish a second story.