To create or model a process, you need to have a business process in the first place. After all, a business process is an ArchiMate object that you can further develop in BPMN.
Click here for the guidelines on how to create a new object.
There are two options for creating a BPMN view:
From a business process
Click on a business process object and open the object properties. For an explanation about these tabs, click here.
Go to the Views tab:
Click the blue New BPMN view button on the right-hand side of the screen. You will be navigated to the new view.
From a view
Click the Main menu and select Views
Click the icon
for creating a new view.
Select Process.
Enter the business process you want to use:
Select OK