BPMN Sub Process
A Sub Process is used to hide or reveal additional levels of detail for your process.
There are two types of Sub Process; expanded and collapsed.
Collapsed Sub Process
If a Sub Process is collapsed, it's represented by a single icon on screen. You can add timing information to represent an approximation of how much time this sub process would usually take to execute, but the steps that would be inside the sub process aren't mapped out seperately.
If the detail of what happens in the Sub Process is not vitally important to the problems in your process you're simulating, then this is the best way to represent it.
Expanded Sub Process
If a Sub Process is Expanded then all the elements within the Sub Process are mapped out explicitly. You can see the elements within the Sub Process in a floating window, or in a seperate tab depending on the settings you've selected.
This set up is really useful when you want to simulate the detail of the sub process but also want a simple high level view of your process.
See Also
BPMN simulation features are only available in Simul8 2012 and higher.