Nope! You are not charged simply by downloading the app.
You are free to navigate and explore the app to get a feel of the content within, and you are also able to watch any preview videos that are available.
If during checkout, you inputted your credit card, then that means you have agreed to begin your free trial and will be automatically charged after your free trial ends.
To view, edit or cancel any active subscriptions or purchases, please follow these instructions here.