May I know how and when to implement commit and roolback?

I got a header file and detail file. I follow the clarion invoice
example to implement it. But I can't find a way to implement commit
and rollback.

May I know how to achieve it? Or clarion invoice example can't
implement since every time is direct write to disk?

Why Clarion not come with sample with commit and rollback? Where can I
get some sample?

Nelson