I've installed SQL Developer on my system. No connections are being shown in my system yet. How do I create a new connection. Must I create a database first? If yes, then how do I create a new database. The SQL Query Editor window is not opening because there is no connection. All of this because there is no database. How do I create an empty database and then connect to it.
This tutorial should help you:
Getting Started with Oracle SQL Developer
See the prerequisites:
Unlock the HR user. Login to SQL*Plus as the SYS user and execute the following command:
alter user hr identified by hr account unlock;
Download and unzip the sqldev_mngdb.zip file that contains all the files you need to perform this tutorial.
Another version from May 2011: Getting Started with Oracle SQL Developer
For more info check this related question:
How to create a new database after initally installing oracle database 11g Express Edition?