In this tutorial How to Setup Read Only Domain Controller For Windows Server 2008 R2 is shown.
Firstly you have to install windows server 2008 R2 server
Configure Network Card (provide a static IP address and DNS)
promote to a domain controller using dcpromo command
Click Next to continue
Select the option: Add a domain controller to an existing domain
Provide the user credentials to perform the installation
Select the domain for the additional domain controller
Select a site
Select following options
Keep the locations for AD DS database, log files and SYSVOL as it is
Provide DSRM password and select Read Only Domain Controller (RODC)
Directory Services Restore Mode (DSRM) is a special boot mode for repairing or recovering Active Directory. It is used to log on to the computer when Active Directory has failed or needs to be restored.