What happens when the packets sent from a computer (at the application layer) reach various network nodes local computers, remote computers, local attached routers/switches, remote routers/switches, hubs, etc.?

Please discuss what network nodes of different types know about the application file being transmitted (based on what information is provided in the header at the OSI layer at which that node operates) at each level of reassembly (i.e., viewing the frame packet only, reassembling frame packets to recreate the IP packet, reassembling the IP packets to recreate the TCP or UDP packets, and reassembly of the TCP/UDP packets to regenerate the full transmitted file) and how that information (provided by the data in the header) might be used by the node to provide network services.