query insert the TRANSACTION, when there is a lock on the table?thank u very much

hi

  i had the code liek this:

BEGIN TRANSACTION;

insert .........

COMMIT TRANSACTION;

  i'd like to ask,when there is a lock on the table?

  when the query of insert  is executed,or when the query COMMIT TRANSACTION is executed?

   thaank u very much in advance ur kindness help

best regards

martin