The Internet is a global network of interconnected computer networks that communicate using a shared set of protocols. It is not a single system owned by anyone; it is an agreement about how independent networks exchange data.
How data travels
Information is broken into packets. Each packet carries a destination address and travels independently across routers until it reaches its target, where the packets are reassembled. If a packet is lost, it is re-sent.
The two central protocols are IP, which handles addressing and routing, and TCP, which ensures that data arrives complete and in order. Some applications use UDP instead, trading reliability for speed — video calls, for example.
Names and addresses
Machines communicate using numeric IP addresses. The Domain Name System translates human-readable names into those numbers. When a name is typed into a browser, a chain of DNS servers is consulted before any content is requested.
The web is not the Internet
The World Wide Web is one service running on the Internet, based on HTTP and HTML. Email, file transfer, messaging and video streaming are separate services using the same underlying network.
Layers
The design is deliberately layered: physical transmission, network routing, transport, and application. Each layer depends only on the interface of the one below it, which is why the Internet has absorbed decades of new hardware and new applications without being redesigned.
Security by addition
The original protocols were built for a small, trusted research network and contain little security. Confidentiality and authentication were added later — TLS for encrypted connections, DNSSEC for name integrity, and various filtering systems. This retrofit explains many of today's structural weaknesses.