Let us understand each component that makes up the simulation of OMNeT++.
In OMNeT++, a Network is an object that defines the network and holds modules, submodules, and compound modules. The Network object allows those different types of modules to talk to each other via channels.
When you run your network simulation, the Network object will look like the following:
I have called this Network object My_Network.
A Module object in OMNeT++ is a component that sits inside a Network object and is able to send messages to other Module objects. In your simulation, this could be a router, a webserver, ...