How to Make a Copy of a database?
I am assuming that by mirror copy ==> you mean at the point when the database full backup was taken.

If that is not the case, then for near to realtime copy of your database, I would suggest transactional replication.

Also, if you are using enterprise edition, then you can leverage the benefits of database SNAPSHOTS.

Step 1: Make a FULL database backup

backup database database_name to disk = 'path to backup drive' with copy_only, stats =10
-- ,compression (sql server 2008 R2 and up, compression is available in standard edition as well).



  e.g. path to backup drive = D:\backups\db_name_FULL.bak


Step 2: Restore the backup taken in step 1 with move.

restore database database_name_mirror
from disk = 'path to backup drive'
with stats =10, recovery,
move 'Logical_Data_FileName' to 'Physical data file location.mdf',
move 'Logical_Log_FileName' to 'Physical log file location.ldf'


Logical file name can be found using sp_helpdb database_name or restore filelistonly from disk = D:\backups\db_name_FULL.bak

e.g. 

restore database database_name_mirror
from disk='D:\backups\db_name_FULL.bak'
WITH move 'database_name_Data' to  'D:\Data\database_name_mirror_Data.mdf',
move 'database_name_log' to  'L:\logs\database_name_mirror_log.ldf';
GO