If you are ready in the preview screen (you set desired rules / set actions for work items individually), click on Save button to finish importing. The page is navigated back to the home page of the trackers, and an information dialog shows, how many work items are imported. Work items will be created according to their actions (import to the current tracker, import into another tracker, etc.). Parent-child relation also remains if work items imported into a common tracker.

If child elements are imported into another tracker, a depends on type association will be created between the work items. Furthermore if some fields of the tracker of the child item can accept work items from the tracker of the parent item, it will be also filled out (For example, if parent item is imported into tasks tracker, its child item imported into test cases tracker, the verifies field of the child item will contain the parent item, because verifies field can accept work item from tasks tracker).