A House Network is a core functionality of ODOS, and is used for both the Storage System and the Collection System.
Simply put, a House Network is a cell you create in which you put activators called Room Markers (ODOSRoomMarker). All the different features of ODOS connect to those markers to create the network.
Room Markers are a way to group your displays into smaller subgroups. You can use them to enable or disable entire groups of displays, if you so wish (in the case of house upgrades, for example). They can be a good way to keep things organized, especially if you have many displays.
When creating Room Markers, be sure to give them a unique name (to find them easily), and to mark them as Persistent References.
Network cells are also where you place the main container of the Storage System (ODOSStorageMAIN). See Storage System for more info.
You can have multiple networks in one mod. Simply make a new cell and new activators in that cell. Connecting displays to those activators will be in a different network than the first.