Throughout the Developer's Guide, you will see the word "protocols" mentioned. There are two general types of protocols that will be discussed. The first type of protocol will be referred to as networking protocols. They are lower level protocols which define how data is exchanged between two systems. The two networking protocols that will be discussed are the User Datagram Protocol (UDP) and the Transmission Control Protocol (TCP).
There are also application protocols, which use the networking protocols to communicate. Application protocols deal with a specific type of functionality. For example, the File Transfer Protocol (FTP) is used to upload and download files, while the Simple Mail Transfer Protocol (SMTP) is used to send e-mail messages. Conceptually, you can think of the networking protocols as defining the rules for how programs can communicate with one another over the Internet. The application protocols operate at a higher level, defining the rules for how a specific kind of task can be carried out, such as transferring a file from one computer to another.