Question: I've installed Drupal Commerce module, I got show cart block in header. If I click on it takes to cart page. I need a pop up of cart page on clicking show cart.

Answer: 
Try the [Commerce Ajax Add to Cart](https://www.drupal.org/project/dc_ajax_add_cart) module.

> 
> Using this module you can ajaxify the add to cart operation. The updated cart
>  will be displayed without page refresh and a popup message will be shown after you add an item to cart. You can customize the look of the blocks using its template files.
> 
> 
>
Along with Krishna Mohan suggestion you can try [Commerce Ajax Cart](https://www.drupal.org/project/commerce_ajax_cart).

This module adds a pop up cart that is AJAX handled.