Hi
server 2012 r2 join domain;
- Right click on "This pc" select "Properties"
- On screen men select "change settings"
- on system propertise men click "change"
- computer/domain changes men select member of "domain" enter the necessary cridentals,
After join to need to be an ADC follow these steps
Server 2012 r2 add Adittional Domain COntroller
- Server Manager->Add roles and features install "Active Directory Domain Services" when instalation done,reboot server
- server manager->"Promote this server to a domain controller"
- "Add a domain contoller to an existing domain"
- set the DNS and GC configuration and follow the steps
also you can check this step by step article;
http://kpytko.pl/active-directory-domain-services/adding-additional-domain-controller-windows-server-2012/