This lesson series will step through the OSI 7-Layer Networking Model

• Physical
• Data Link
• Network
• Transport
• Session
• Presentation
• Application

https://en.wikipedia.org/wiki/OSI_model

The network layer adds the ability for cross-network addressing (IP Addresses). It allows packets to be routed across different layer 2 networks, via L2 Frame encapsulation and forwarding decisions using routes and route tables. Its Layer 3 which allows the internet to function.