Most protocols are defined in RFCs (request for comments), but some are proprietary and closed. Google "TCP RFC" and you'll find several RFCs that cover various aspects of TCP.

You can write your own protocols in programming languages that support network programming if you want.

I think you mean TCP transmits information reliably, not securely.

You need to review the OSI and TCP/IP networking models. FTP is an application-layer protocol while TCP is a transport-layer protocol. FTP runs on top of TCP.

Check out Wikipedia and the RFCs for further reading. If you're looking for a textbook, grab a Network+ or CCENT book.

Welcome to the forums.

I think this is the same question I asked myself a while ago :-)

As far as I can work out, what a protocol -exactly- is, is a text saying 'lets have it work like so, so and so'.

It's not programmed, it's not source code. It's an agreement of the form: when I send you those bits, you send me either those bits or those bits (or packets) back, within x seconds.

Every programmer can then make his own implementation of the protocol.
For example, when a company starts making a router, they look at the texts (RFC's) to see what is expected from them, what they need to send to other routers (router protocols), what they get from connected pc (DHCP requests for example), and they try their best to make it work out (some better then others).

If you would make a new car, you have to do the same: look at the rules and regulations to see how many lights you need, seatbelts, minimum specifications of brakes, etc. Those rules and regulations would be 'the protocol'.

This is all just 'as far as I know', me = newbie :-)

Thank you all for your posts I really appreciate it. 
These replys were way more helpful than any I got at school.

speaking of school, have you ever been to this site? http://www.hackerhighschool.org/ it explains some basic things (come to think of it, probably also protocols) you might want to know about networking and other (offensive) security stuff. glad we could help!

WOW, that brings back memories! i have seen that video about 7 years ago in class as an introduction for my bachelor. Corny, but great video!