A host can imagine the family of a laptop, which is the client, Host B can be thought ran on the server nginx
Host A sends a http get request to host B which experienced request.
In the data stream:
The application layer sends a get request, the transport layer, the browser opens a port, windows task manager to see this process the port and recorded, as well as the 80 or 443 nginx recorded.
Network layer recording ip host and target nginx our host's ip (public ip), through to the link layer Ethernet router to reach our own home, where we record the next period of operators ip, after a final jump to the wide area network where the host server B, the final packets link layer, network layer, transport layer, the operating system knows the port 80 is open to nginx, http application layer in the state machine to process the request.