Where to find good tutorial(s) about TCP and UDP programming

I started to learn TCP sockets programming. So far I'm able to send the message from the client on one host to the listener on another, and get the response back from the listener.

That was when I began to realize that I have to learn a lot before I could start using sockets in any useful way.

 

Trouble is that I was able, so far,  to locate two types of tutorials. 

 

- the tutorial delves straight into code but explain no whys and hows along the way. Utterly useless!

 

- the tutorial starts at the point when Andrew S.Tannenbaum was potty trained. It ends up with undecipherable instructions on how to build the largest quantum computer in the community where you live. Perhaps one can find a paragraph or two on sockets. Which are useless, again.

 

So I am looking for suggestions for TCP and UDP tutorial (preferably online), with step by step explanations of their use, and possible use scenarios (i.e. when and why a single port is adequate, and when and why multiple ports are in order). The tutorial should be well accompanied by code which explains the finer point of it, preferably C# (but Python, pseudocode, and even Pascal are OK, too).