
Explanation/Reference:
Note:
* Before you install Microsoft Exchange Server 2013 on any servers in your organization, you must prepare Active Directory and domains.
* Prepare Active Directory and domains
1. From a Command Prompt window, run the following command.
setup /PrepareSchemaorsetup /ps
2. From a Command Prompt window, run the following command.
setup /PrepareAD [/OrganizationName:<organization name>]orsetup /p [/on:<organization name>]
3. From a Command Prompt window, run one of the following commands:
Run setup /PrepareDomain or setup /pd to prepare the local domain. You don't need to run this in the

domain where you ran Step 2. Running setup /PrepareAD prepares the local domain.
Run setup /PrepareDomain:<FQDN of domain you want to prepare> to prepare a specific domain.

Run setup /PrepareAllDomains or setup /pad to prepare all domains in your organization.

Reference:
Exchange 2013 Prerequisites: Exchange 2013 Help
Exchange 2013, Prepare Active Directory and Domains