Q: How do I... Use sockets? Do networking? Write client/server applications?
A: All of these questions are outside of the scope of this list and have much more to do with the networking facilities which you have available than they do with C. Good books on the subject are Douglas Comer's three-volume Internetworking with TCP/IP and W. R. Stevens's UNIX Network Programming. There is also plenty of information out on the net itself, including the ``Unix Socket FAQ'', and "Beej's Guide to Network Programming".
(One tip: depending on your OS, you may need to explicitly request the -lsocket and -lnsl libraries; see question 13.25.)