The creation of your own app and widget modifications essentially involves three steps:
Prepare the content (images, videos, PDF documents, logos, icons and colors (Keycolors) ) for your CI. Further information can be obtained in the corresponding app documentation as well as in the section about data formats.
When you create a mod you link your data with the corresponding app.
Open your mod in AppSuite and check your content and designs. Alternatively you could also create a mod conveniently on your PC or laptop first and then import it to the target system.