Dear Vinoth,
The question is redundant and amply answered by the available material that we already pointed to.
For a final clarification:
The only way to make a modification to a document is to open a transaction on it. The transaction is bound to that single document. The transaction can optionally be encapsulated in one or more (nested) transaction groups.
The only way to cancel a modification is to roll back the transaction or one of the encapsulating transaction group.
I hope that is clear now.
Cheers,
Jeremy