A very simple way...
1.
Simply write the operating instructions or the help section of your app in MS Word. Format the background colour, fonts, font sizes and text colours there. Use the hyperlink function to quickly navigate to other places in the document.
2.
Save this Word file as an original and as an HTML file. Make sure that you use UTF-8 as the encoding when saving with HTML under Extras, Web Extras, Encoding (this setting is normally saved by Word with the document). This avoids problems in the display of special characters.
3.
When you start your app, load the HTML file from the assets into a webview. Done.
Advantage:
You can quickly keep the in-app documentation up to date; even a FAQ section or a version history are conceivable. All you have to do is open the HTML file with Word and save it.
Disadvantage:
It is not so easy to integrate pictures.