The point of a database is to store and retrieve data. These basic utilizations of a database are essentially application specific. Your not generally gonna interact with your database by firing up SQL*Plus every time you need to get a phone number from your address book.
Oracle provides a wide variety of diffrent methods of interacting with the database. There is obviously SQL*Plus for traditional SQL interaction via CLI. We can also use PL/SQL for scripting purposes. PERL can be used via the DBI/DBD interfaces. There is a C API called the OCI (Oracle Call Interface) which is used by most Oracle tools. There is a C++ interface called OCCI (Oracle C++ Call Interface). Plus there is a full compliment of Java, .Net, OLE, blah blah blah interfaces if your into that sorta thing. Your C and C++ apps can also utilize Pro*C and Pro*C++ precompilers for embedding SQL and PL/SQL in your code.
Lets take a look at some of the interfaces. We've already used SQL*Plus in the last chapter so we'll skip that one.
You can find documentation on these interfaces in the Oracle Documentation Library, where you should particularly have a look at Application Developer's Guide - Fundamentals to get started: