It’s not hard to do, but like drawing UML diagrams, it is sort of detailed, and you want to get the notation right. You can read the (very long) spec at http://www.omg.org/bpmn. Read books and get tools from various vendors (https://bpmn.io offers many wonderful examples, and Visio and LucidChart work well) to help you draw proper BPMN diagrams. Figure 6-5 shows an example.
