The basic requirement in Jdeveloper is to connect to database and execute queries in Jdeveloper. We'll see how to do it in below steps.
1. Check if 'Database Navigator' palette is open in Jdeveloper. If now, cick on 'View' and select 'Database Navigator'.
2. In the 'Database Navigator', Right click 'IDE Connections' and select 'New Connection'.
3. In the 'Create Database Connection' window, give Name for the connection, select the type of DB you want to connect.
4. Give the connection details for the DB. You can give database connection URL by checking 'Enter Custom JDBC URL'. Test your connection and click 'OK'.
5. Now, you can see the newly created DB under 'IDE Connections'. Select it and Right Click and select 'Connect'.
6. It'll open SQL editor window where you can type and execute your queries (It is same as Oracle SQL Developer).
7. Alternatively, you can also connect to DB by clicking on the 'SQL' icon and selecting the appropriate DB connection.