Hi,
all jBackend documentation is available here:

www.selfget.com/documentation/jbackend-joomla30.html

Each module has its own chapter with ALL available API. For the content module you can look here:

www.selfget.com/documentation/jbackend-joomla30/content-module-api.html

A you can see, is not possible yet to use jBackend to write content. We are trying to cover the most used extensions and the most common tasks. So, adding API to create articles maybe will be availble in the future, but in our opinion this is not a "must have" for now.

Moreover, jBackend could be extended by users and plugin structure is well documented:

www.selfget.com/documentation/jbackend-joomla30/developers-guide.html

Kind regards,
Luigi