The endpoints are the visible part of your videoconferences. They are also known as codecs. They have a camera and a small networking component for two participants – this provides a point-to-point conference as long as both sides have videoconferencing hardware.
The network is the infrastructure that allows you to communicate with several endpoints to hold a multipoint videoconference. The network is used to send information from one endpoint to any number of others. And it allows the endpoints to communicate with each other.
As with all complex technologies, it is not enough to install equipment and infrastructure and expect it all to magically start working. You need experts by your side, connecting people and managing the network.