Why does my office computer send packet #1? what device responds by sending back packet #2? what information does my office computer learn from packet #2?

The office computer is part of a network.

The server responds with a packet when a request packet is sent by a client.

The computer confirms the IP address and port number to retrieve the encapsulated data, for a specific application in the system.

Explanation:

The computer network is the communication of two or more devices. There are two forms of network, there are peer to peer and client/server networks.

The peer to peer network allows for each computer to send and receive data, while the client/server network have a dedicated server to send resources to clients that request for it. Data transferred are encapsulated in the network, transport and data-link layer PDU headers and would be decided in the destination system to retrieve the data.