I want to add step before final checkout is done to show order summary (address, shipping details, and payment method etc. which are selected by customer). how to implement? Please help.
Not easily. Every payment method handles its own order placement (with its own place order button and corresponding JS code). Adding a post-payment step would require overriding that JS for every payment method you offer to account for the additional step, in addition to the normal process of adding your knockout component.
Magento 2 dev docs detail the process for adding a checkout step here: http://devdocs.magento.com/guides/v2.1/howdoi/checkout/checkout_new_step.html
The doc suggests you can set
sortOrder > 2 to have your added step after payment, but as I noted each payment method handles its own submission (assuming it will be the final step). It's unlikely adding a review step will be as simple as the doc lays out.