Nothing, to get you acquainted with the app - when you use an initial free trial that is available with few plans.
When you decide to use the app like a pro, you need to select a plan from the below options:
- Weekly plan - easy to try, as little as USD 2.99 per week.
- Monthly plan - free for 3 days and then about a pack of candy or jelly beans, that is USD 8.99 per month.
- Yearly plan - USD 24.99 per year, which is effectively just about 50 cents a week.
[above prices are true at the time of writing this, can be different from time to time and other countries]
The prices are revised (mostly reduced) from time to time. So, you can refer to exact pricing:
- On the AppStore page where the DrawingPad is listed, you will find under In-App Purchase expansion
- Within the app when you open it and start drawing, you will be displayed a screen to select the preferred option.
Your AppStore account takes care of its fees, and the plans renew automatically (unless it is one time). Also, you can get the receipts via your Apple account that you may need.