Creating a new database and new connection in Oracle SQL Developer

Creating a new database and new connection in Oracle SQL Developer

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.