We have some resources you can access within the app. Open the asset drawer and tap the shopping cart icon to access the "shop" (don't worry everything is free).
You can download the few characters we have there. Check out the documentation in the Learn tab. We have a creating a platformer game tutorial that shows you this process (https://hyperpad.zendesk.com/hc/en-us/articles/205716699-Part-2-Importing-your-assets)
Additionally, when you first launch hyperPad there should be an interactive tutorial which shows you around the app, and includes downloading assets.
Also you can use other apps from the app store to draw and import custom graphics and characters.