This manual, as well as other documentation on the CUBA platform, are available at https://www.cuba-platform.com/manual.
CUBA business process management subsystem is based on the Activiti framework, therefore general knowledge on the framework is beneficial. See http://www.activiti.org to learn more about the Activity framework.
An executable process description employs the BPMN 2.0 notation. Consequently, it is assumed that the reader is familiar with the notation. More information about BPMN 2.0 specification can be found at http://www.bpmn.org.