These transaction are required to fulfil certain characteristics and they are :
Atomicity: The transaction is either performed entirely or not performed at all.
Isolation: The transaction should not be interfered by any other transaction executing concurrently.
Durability: The changes made by the transaction should be permanently committed in the database.
Consistency preservation: If the database was consistent before the execution of the transaction .It should remain consistent after the complete execution of that transaction.
There are two types of transactions: explicit and implicit
Explicit are those that need to be specified like : commit and roll-back
Commit transaction signals that the transaction was successfully executed and the changes/ updates (if any) made by the transaction have been committed to the database and these changes cannot be undone.
Roll-back signals that the transaction was not successfully executed , and the changes/updates made by the transaction have to be undone.
Implicit transactions are those that mark beginning and end of the transaction, each statement like update, delete , insert run within these implicit transactions.,However, you can explicitly specify the beginning and ending of the transaction by "begin transaction" and "end transaction" statements respectively. All the statements within these two boundaries will be marked as one transaction.