Sorry - still don't understand BIP39 (etc) - how does a static phrase generate?

Sorry - still don't understand BIP39 (etc) - how does a static phrase generate dynamic addresses? I noticed while using my Ledger Nano S, that every time I make a bitcoin deposit into the Ledger, it generates a new deposit address. The entire Ledger is represented by a 24 word phrase - how does a static phrase generate addresses dynamically?

The only thing that makes sense to me (and I am 20 years in the IT industry) is that the 24 word phrase represents a "pointer" in the distributed network and the distributed network is generating the addresses that it stores against the 24 word phrase key pointer?

For example, when you create some of these alt-coin wallets, you are asked to enter an 80 character seed. From that seed an address is created. You deposit your coins, and can create a new wallet from that same 80 character seed. So a static 80 characters is used to generate a seed that stores dynamic information (your coin deposits), but the management of that dynamic information is by the NETWORK. Is this how BIP39 (etc.) works? The 24 word phrase is used by the network as a pointer to a database of wallets?

Thanks!!