There are absolutely 3 terms you always need to remember while working with SQL Developer.

A Transaction – is a group of SQL statements that must all be executed together. By default, Oracle adds INSERT, UPDATE and DELETE statements to a transaction

The COMMIT statement commit the changes you have made. In SQL developer the option is F11

The ROLLBACK – it rollsback the changes made by transaction. In SQL developer the option is F12

When you do not COMMIT changes explicitly, when you exit SQL developer, it rollback the changes made to database

There is an Auto commit option in SQL Developer, In Worksheet Parameters node, check the check box “Autocommit SQL WorkSheet”