A transaction is a set of instructions that are together considered as a Single Unit
It should all either be executed successfully or none should be executed. On Commit only all DML commands are saved permanently.
COMMIT Command
WORK is optional and is used to make the command SQL compliant. The command has the same output with or without WORK parameter.
COMMENT is used to add an message to the commit to easily identify it later. It is also optional. It is used to identify the comment in the DBA_2PC_PENDING table
Oracle / PLSQL: COMMIT Statement
COMMIT [WORK] [COMMENT 'your comment'];ROLEBACK Command
It reverts the state of the system to the last COMMIT point.
ROLLBACK;SAVEPOINT Command
Specifies a point in a transaction to which we can roll back later.
SAVEPOINT ABC;