You need to restore the database.
1. Install SQL Express, make sure to have all the settings for file locations etc. right
2. connect to the SQL Server Express instance
3. create a sql script that restores the database
Sample:
create database myDatabase;
go
RESTORE DATABASE myDatabase
FROM DISK = 'c:\pathToBackupFile\myDatabase.bak';
Look here for options of the restore command:
http://msdn.microsoft.com/en-us/library/ms186858.aspx[
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