Consider this common lab scenario you might build in Cisco Packet Tracer:
You cannot directly connect a Copper port to a Fiber port using a standard cable. This is where the enters the scene.
[PC1]---Copper---[Switch A]---Fiber---[Switch B (acting as media converter)]---Copper---[Router]
Always check the cable types (Copper straight-through vs. Fiber) when creating your link. Packet Tracer will give a red "link down" icon if the connection is invalid—a sign that you may need a different interface or a simulated converter.
Look at the bottom-left corner of the Packet Tracer interface.
Here is a comprehensive guide on how to implement media conversion functionality within Cisco Packet Tracer. Why Media Converters are Needed in Networking
