Let me answer the first part only as I could not get the context of the second part -
Packet Switching Fundamentally, a packet switched network establishes a path from host to host over a shared medium. Packet switching relies on shared resources to transfer data across the network.
Circuit Switching A circuit switched network is greedier with its resources but ensures the availability of those resources. From point A to point B you have allocated specific resources for the duration of the conversation. Host A and Client B have sole rights to leverage those resources until terminating the call.
In the past circuit switching technologies existed mostly for voice communications. In today’s day and age, voice traffic is also sharing the road with data networks in a converged packet switched environment.