Triggers are implicitly started (executed) by Oracle when a triggering event occurs, regardless of which user is connected or which application is being used.
You can define triggers under the "Table Triggers" tab.
Creating or Deleting a Table
All database tables will be listed in the "Database Tables" screen.
You can drop (invalidate) tables as "Database Status" -> "Current" or create tables with "Database Status" -> "Not Created" using the corresponding "Drop" and "Create" buttons.