The world of network communication is governed by a set of protocols (rules and regulations) in order to function as intended. Protocols govern the transmission of network packets/segments/frames over a communication channel between endpoints. In order to understand how network packets stick together, forming a stream of traffic, we need to understand the basics of the networking that is the TCP/IP model. The TCP/IP model was originally known as the DoD model, a project that was regulated by the United States Department of Defense. All of the communication that we witness over the internet and other networks happens only through TCP/IP.
The TCP/IP model takes care of every part of packet's life cycle, namely, how a packet comes to life, how a packet is generated, how information pertaining to packet gets attached data payload (PDU), how it is routed through intermediary nodes, linking with other packets and so on.
It is strongly recommended to do some self-study on TCP/IP and how it functions, before you proceed ahead, as this book requires decent amount of familiarity with protocols.
