How to work with Sockets.

Question

Hey there.
I am trying to make a new program, I am new with Sockets because it is kinda hard, and I need your help on making these things [Server and Client]:

I want to send from the server to the client a string and when the client gets the string "doitall" it will show a messagebox on the client.
If you can't help me with that can you please give me something that can help?
a tutorial or something? because I don't know how to make that the client gets a
string too, only the server..

I think I need to do this with Asynchronous Socket
Thanks in advance!