Create/Show relationship between parent and child term in Drupal Taxonomy

Possible Use-Case : You want to show a list of "Countries" and there related "Cities". But you want only related cities to be shown on the page .
 To do this place country as parent term and all the cities as sub-term. So construct a vocabulary like this :

- Delhi
 - Rajashtan
- Chandigarh
- Gujrat

- Alabama
- Alaska
- Georgia
- Illinois

Then use simple module called "Simple Hierarchical Select" or you can also use "Hierarchical Select"
But hierarchical select has more functions but if you have taxonomy related task only then you can use only SHS as for the above use-case.

Now go to the content type -> manage fields -> select term reference-> simple hierarchical select Or create a field like this if you haven't created.
Now go to your views or create a view if you haven't already created => select the "your-field-name" (hierarchical select ) from filters and force it to some depth. Expose this filter for users.

Then it will show first country name and then child term which are city names.