In many companies processes are described in text documents or freely drawn diagrams that everyone reads slightly differently. BPMN provides a common language: every symbol has a defined meaning.
The basic elements
Events mark the start, intermediate steps and end of a process, such as receipt of an application or expiry of a deadline. Activities are the work steps. Gateways split and merge the flow by condition or in parallel. Sequence flows connect elements within a flow; message flows show exchanges between participants. Pools represent organisations or systems, lanes represent roles within them.
What BPMN is good for
Analysing a current process before digitalisation, specifying a target process as part of requirements, agreeing responsibilities between departments and as a basis for automated execution in a workflow platform. In a workflow platform evaluation, BPMN models are often the yardstick platforms are measured against.
Levels of detail
Not every model needs every element. For alignment with management, an overview with the main steps and responsibilities suffices. Automation needs precise gateways, events and data objects. The level of detail should fit the purpose; overly detailed overviews go unread, overly coarse models cannot be implemented.
Typical mistakes
Gateways without conditions on outgoing flows, processes without clear start and end events, sequence flows across pool boundaries instead of message flows, and models describing the system rather than the process. A good test: can someone from the business follow the model without explanation?