Primary actions, also called workflows nodes, serve as the entry point or top-tier node of a process or sub-process. An action serves as a bridge, linking an event listener with a process or sub-process. Every process has a root-level primary action or starting point (represented as a lightning bolt in the workflow explorer and the process canvas). For more information, see "Using workflow explorer".
These actions have few attributes, but are connected to event listeners which are responsible for starting processes. See "Event listeners".
You can have additional primary actions within your processes. These primary actions represent the start of another process and can be considered a sub-process of the current process. You can double-click these additional primary actions, which will launch the process associated with that primary action (workflow). In this manner, processes can exist independently or be part of other processes.