Import .bak file to a database in SQL server

On Microsoft SQL Server Management Studio 2019:

On Restore Database window:

1. Choose Device

2. Choose Add and pick target file

3. OK to confirm

4. OK to confirm restore

Although it is much easier to restore database using SSMS as stated in many answers. You can also restore Database using .bak with SQL server query, for example

RESTORE DATABASE AdventureWorks2012 FROM DISK = 'D:\AdventureWorks2012.BAK'
GO

In above Query you need to keep in mind about .mdf/.ldf file location. You might get error

System.Data.SqlClient.SqlError: Directory lookup for the file "C:\PROGRAM FILES\MICROSOFT SQL SERVER\MSSQL.1\MSSQL\DATA\AdventureWorks.MDF" failed with the operating system error 3(The system cannot find the path specified.). (Microsoft.SqlServer.SmoExtended)

So you need to run Query as below

RESTORE FILELISTONLY 
FROM DISK = 'D:\AdventureWorks2012.BAK'

Once you will run above Query you will get location of mdf/ldf use it Restore database using query

USE MASTER
GO
RESTORE DATABASE DBASE 
FROM DISK = 'D:\AdventureWorks2012.BAK'
WITH 
MOVE 'DBASE' TO 'C:\Program Files\Microsoft SQL Server\MSSQL10_50.DBASE\MSSQL\DATA\DBASE.MDF',
MOVE 'DBASE_LOG' TO 'C:\Program Files\Microsoft SQL Server\MSSQL10_50.DBASE\MSSQL\DATA\DBASE_1.LDF', 
NOUNLOAD,  REPLACE,  NOUNLOAD,  STATS = 5
GO

Source:Restore database from .bak file in SQL server (With & without scripts)