Internet protocols
In this context, there are three layers of protocols:

at the lowest level is IP - the datagram which carries a block of data from one node to another
next comes TCP & UDP - the protocols by which one host exchanges data with another - the former making a virtual circuit giving some level of guarantee of reliability, the latter being a best-effort connection-less transport
on top comes the application protocol - the specific messages or data stream used by the application running on the hosts to talk to each other.
Unlike older communications systems, the Internet protocol suite was deliberately designed to be independent of the underlying physical medium. Any communications network, wired or wireless, that can carry two-way digital data can carry Internet traffic. Thus, Internet packets flow through wired networks like copper wire, coaxial cable, and fibre optic; and through wireless networks like Wi-Fi. Together, all these networks, sharing the same high-level protocols, form the Internet.

The Internet protocols originate from discussions within the Internet Engineering Task Force (IETF) and its working groups, which are open to public participation and review. These committees produce documents that are known as Request for Comments documents (RFCs). Some RFCs are raised to the status of Internet Standard by the IETF process.
Some of the most used application protocols in the Internet protocol suite are IP, TCP, UDP, DNS, PPP, SLIP, ICMP, POP3, IMAP, SMTP, HTTP, HTTPS, SSH, Telnet, FTP, LDAP, SSL, and TLS.
Some of the popular services on the Internet that make use of these protocols are e-mail, Usenet newsgroups, file sharing, Instant Messenger, the World Wide Web, Gopher, session access, WAIS, finger, IRC, MUDs, and MUSHs. Of these, e-mail and the World Wide Web are clearly the most used, and many other services are built upon them, such as mailing lists and blogs. The Internet makes it possible to provide real-time services such as Internet radio and webcasts that can be accessed from anywhere in the world.
Some other popular services of the Internet were not created this way, but were originally based on proprietary systems. These include IRC, ICQ, AIM, and Gnutella, although all of those mentioned now have Free implementations, which in some cases are the most commonly used.

Internet structure
There have been many analyses of the Internet and its structure. For example, it has been determined that the Internet IP routing structure and hypertext links of the World Wide Web are examples of scale-free networks.
Similar to how the commercial Internet providers connect via Internet exchange points, research networks tend to interconnect into large subnetworks such as:

GEANT
GLORIAD
Internet2
JANET (the UK's Joint Academic Network aka UKERNA)
These in turn are built around relatively smaller networks. See also the list of academic computer network organizations
In network schematic diagrams, the Internet is often represented by a cloud symbol, into and out of which network communications can pass.

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