How to create connected models

Hi,

User can connect objects or models by using the connection lines, as far as I understand, this is what it called "connected objects or modules" in a process model.

But it turns out that in "connected objects" it shows only the assignment fo the process and in "connected models" not every model connected are shown. I wonder if the  "connected objects" or "connected models" here refers to other explanation?

Also, I would like to ask how to connect process steps with IT system.

Thanks in advance.