TCP/IP is a big chapter and one that can't be analyzed in a few paragraphs. To help you get the big picture, we'll keep things simple and focus on the details you need, to ensure you get a proper understanding.
The term "TCP/IP" stands for Transmission Control Protocol / Internet Protocol and refers to a number of protocols. The "IP" part of the term, which stands for Internet Protocol, is used by TCP and UDP, to transport them from one network to another. Think of IP as a sort of high-way that allows other protocols to get on and find their way to other computers. TCP and UDP are the "trucks" on the highway, and the "load" they are carrying are protocols such as HTTP, File Transfer Protocol (FTP) and more.
As you can understand, TCP and UDP are transport protocols used by protocols such as FTP, HTTP, and SMTP. While both TCP and UDP are used to transport other protocols, they have one significant difference; TCP offers guaranteed data transportation, whereas UDP doesn't. What this means is that TCP has a special mechanism that ensures data is safely transferred without errors from one point to another, whereas UDP doesn't provide any such insurance.
HTTP (HyperText Transfer Protocol) is a protocol that utilizes TCP to transfer its information between computers (usually Web servers and clients). The client makes an HTTP request to the Web server using a Web browser, and the Web server sends the requested information (website) to the client.
Remember, IP is required to connect all networks; TCP is a mechanism that allows us to transfer data safely; and HTTP, which utilizes TCP to transfer its data, is a specific protocol used by Web servers and clients.
There's a detailed analysis on the protocols, including lots of diagrams to help the understanding process become as easy as possible, on my website: http://www.firewall.cx/protocols.php
I hope things are a lot clearer for you now.
This was first published in August 2007