Can you explain the roles of metric monitoring and distributed tracing in troubleshooting issues online?

Metric Monitoring: Because I have a blind spot in performance optimization and there's another team nearby working on a similar business direction. I am a bit curious, and I hope to learn some basic knowledge about performance, capacity, and stability from this part.
Distributed Tracing: This is what I'm most curious about. When a company has a large number of machines, how do they achieve end-to-end tracing, and what technologies are behind it?