To restore a database from the files you need the data file - MDF, sometimes NDF exist as well, and the log file - LDF.
- Start SQL Server Management Studio
- Right-click the Databases node
- Select Attach
- Click Add
- Select the MDF file you saved
- The LDF file should be automatically added. If not, the 'Not found' message will be shown and you must add the file manually by clicking the ellipsis button

If this fails, try to attach only the MDF file, using the sp_attach_single_file_db function
EXEC sp_attach_single_file_db @dbname = 'AdventureWorks2012Restored' , @physname = N'D:\ApexSQL\backups\CS2.mdf';
If this fails, the MDF file might be corrupted. You can try a third party tool that will read the MDF file and recover your data
ApexSQL Recover is a tool that can read a corrupted MDF file, re-create all objects and recover table records. It can create T-SQL script or create a copy of the database
Disclaimer: I work for ApexSQL as a support engineer