An eChapter within CloudPublish is essentially an extract from an existing eBook. Therefore, in order to create eChapters, it is necessary to first add eBooks.
eChapters are defined primarily by specifying a page range from a parent eBook. Additional metadata can be specified (for example, chapter title, chapter author, etc.) and this can be done either by CSV upload or by using the /ChapterCreate method of the CloudPublish API. The advantage to using the API is that metadata can be automatically copied from the metadata held for the parent eBook (by specifying copy_metadata=1). In both cases, however, the parent eBook ID must be specified.
Given that eChapters are simply extracts from eBooks, it is possible to create items that contain several chapters of a book, or indeed any arbitrary page range.
For more information about other types of metadata, please see these pages:
eChapters and DRM
It should be noted that eChapters cannot have "hard DRM" applied - the only DRM option for eChapters is "soft DRM". More information about the DRM options can be found here.