first, you have to understand the concept of clients and servers in programming.
to program clients (end users) u usually need to know awt or swing (gui stuff) or maybe
applets etc. you need to know how will your clients connect to your server (either through an application youll give them, or thruogh the browser in the internet, or even an applet in a browser). there is a new trend also of using the java web start to distibute the clients applications.
for the server side, u need some tools to access the database u have at your computer. for that u need the
JDBC connectivity to a database server.
if your clients are connecting through the internet using browsers u need to use servlets or jsp to show them html web pages they can surf with through your site.
also, u can use RMI and
EJB for regular application that users can connect to from their own applications u give them.
a last option , would be for small servers to make everything yourself using regular sockets and to send the data yourself across the network.
to sum it up, server side java includes all the API u need to put on the server and allow multiple clients to connect to. that includes: JDBC, Servlets, JSP, RMI, EJB, IDL and corba.
i might have forgotten somthing but thats about it. notice u dont have to know all of the API, just the ones u want to work with.