Here I am showing how you can import SQL database file (in ".bak" format) using Microsoft SQL Server Management Studio:
1) Open Studio and connect to the database.
2) Right click on "Database" listed in "Object Explorer" and select "Restore Database".
3) From the popup select the "device" as "source".
4) Click on button with "..." on the right side, it will open popup which allows you to select ".bak" file. Here you can select more than one file to be restore.
5) Now click "OK" to restore the database. It will take some time to import database depending upon the size of the database and get listed automatically under "database" in "object explore".
Hope it will help someone!!!