Questions about connections and stuff

Well, here I am again with another request related to networks

As I don't seem to understand very well how networking in general works, I would like to ask you a few questions:

• What is a TCP connection, and how does it work?
  
• What is a UDP connection, and how does it work?
  
• What's the difference between a TCP and a UDP connection?
  
• What is a socket?
  
• Can a server send commands to a client through a TCP connection? (asking this because the example in the help file  demonstrates a client sending text to a server)

I hope someone can answer those questions, any kind of help is appreciated

Thanks in advance !