OSI is a seven-layer reference model, Physical, Data Link, Network, Transport, Session, Presentation, Application, created as a design and teaching framework. TCP/IP is the four-layer model the actual internet runs on: Link, Internet, Transport, and Application. They map onto each other: OSI's Physical and Data Link correspond to TCP/IP's Link layer; OSI's Network is TCP/IP's Internet (IP); Transport maps directly (TCP/UDP); and OSI's top three, Session, Presentation, Application, collapse into TCP/IP's single Application layer, because in practice those concerns (session management, encoding, the service itself) are handled within applications and libraries rather than as distinct network layers. The practical takeaway is that the internet is TCP/IP, while OSI provides the shared vocabulary everyone uses, when someone says "layer 7" or "a layer-2 switch," they're speaking OSI numbers even while describing a TCP/IP network. So you learn TCP/IP as what's real and OSI as the lingua franca for discussing it.
Networking & IoT · Interview question
How do the OSI and TCP/IP models relate?
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OSI vs TCP/IP Model
Why networking is split into stacked layers, how the 7-layer OSI reference maps onto the 4-layer TCP/IP model the internet actually runs on, and how encapsulation wraps your data.