How do you create a new database in SQL Developer? I  am a software developer that supports and develops an application that connects to both Oracle databases and SQL Server databases.  I want to learn more about database administration. 

In SQL Studio Manager you can open a connection to a server and then selected the master database and then run a statement like this:

CREATE Database TestDatabase


TestDatabase is then available to connect to on that database server.

However, with SQL Developer you have to connect to a database already created (rather than connecting to the server).  Therefore how do you create a new database in SQL Developer?

I thought I would be able to find my answer by Googling.  However, this was not the case.  There seem to be hundreds of tutorials about creating tables but I cannot find any about creating a database.
The term database has a different meaning in Oracle. The definition of database by Oracle:


  A set of files, located on disk, that store data. Because a database
  instance and a database are so closely connected, the term Oracle
  database is often used to refer to both instance and database.


Oracle Database Architecture

If you wanted to seperate data per application, you could do that by using seperate tablespaces and schemas.

Creating such a database is a complex process, and it is done with DBCA or SQL*Plus on the database server, not with a remote connection:

Creating and Configuring an Oracle Database

In 12c, the multitenant architechture was introduced, that is similar to the concept in SQL Server.

Overview of Managing a Multitenant Environment

If you have a container database, there you can easily create new pluggable databases from SQL Developer, when using a DBA connection.

Managing Pluggable Databases (PDBs) using Oracle SQL Developer