Chain Network is an aggregation of chains, cells (shards), tokens, its ledgers and whitelists (GDB) providing by nodes over the internet or an intranet. Network could be public, where everybody could connect with it, and private where only authorized users could connect with it.
All assets are common to the network. Tokens are declared for the entire network, its impossible to have token only for specified chain or cell (shard). Because of this, ledger is also single for network and could be spread over the different parts.
Every network has its core that seeds it for newbies. This function can be performed by root nodes, archive nodes or it can be temprorary dutie of ordinary node. When the new node connects to seed node it gets the cells list and node lists, then finds the nearest one (or few) and brings up links to them. After that the uplinks update node lists and add the newbie in it.
The network can be broken down by cells (shards) - groups of nodes that has common data, chains and connected with themeselves. More details about cells you can see here.