I have an .mdf file on my local box.
I have SQL Server 2008 Express and SQL Management Studio 2008 Express installed on my local box.
How in the world do I impor
If you do not have an LDF file then:
1) put the MDF in the C:\Program Files\Microsoft SQL Server\MSSQL13.SQLEXPRESS\MSSQL\DATA\
2) In ssms, go to Databases -> Attach
and add the MDF file. It will not let you add it this way but it will tell you the database name contained within.
3) Make sure the user you are running ssms.exe as has acccess to this MDF file.
4) Now that you know the DbName, run
EXEC sp_attach_single_file_db @dbname = 'DbName',
@physname = N'C:\Program Files\Microsoft SQL Server\MSSQL13.SQLEXPRESS\MSSQL\DATA\yourfile.mdf';
Reference: https://dba.stackexchange.com/questions/12089/attaching-mdf-without-ldf