The follwoing are the transaction control statements

COMMIT-
   To make the changes done in a transaction permanent issue the COMMIT statement.
ROLLBACK  -
   Rollbacks the state of database to the last commit point.
SAVEPOINT -    
   Specify a point in a transaction to which later you can roll back..

For example -
insert into tab1(col11,col12) values (val11,val12);
savepoint a;
insert into tab2(col21,col22) values (val21,val22);
savepoint b;

Now if we give a commad -
rollback to a;
then the rows inserted into to tab2 will be roll backed.
Now we can commit the row inserted into tab1 table or rollback the transaction.

Then SET TRANSACTION is an Advanced Transaction Control statement which is supported in SQLJ and to specify the access mode and isolation level of any given transaction.