Transactions (Really Simple)

Hello all,

I would like to use transactions while inserting, deleting or updating
data from my database.

I have read the on-line documentation, but I would like some help.

How could I implement transaction feature to the `insert command' bellow?

-------------------------------
...... which command here?
insert into table1 (field11,field12) values ('value11','value12')
insert into table2 (field21,field22) values ('value21','value22')
...... which command here?
-------------------------------

Thanks in advance,

Marcelo Pereira