Join Server 2012 R2 Core to your Domain
If you are using Server 2012 R2 Core and you wish to join it to the domain, then you can use this simple Powershell command to do it.
Add-Computer -DomainName YOURDOMAIN.COM -Credentials DOMAINUSERNAME -Restart
Note that the -Restart command at the end will automatically restart your server once it has completed the joining process.
Also be aware that you should change YOURDOMAIN.COM to the domain name that you are trying to join and also change DOMAINUSERNAME to domain admin credentials for the domain you are joining.