Hi Everybody, I am beginner to the virtualization, i want know the virtual machine licensing terms for Hyper-V server 2012.

It is free version, but how we can manage the virtual machine license?

How many VMs we can in

Hyper-V server doesn't include any licensing for VMs. You need to have appropriate licensing for the OSs your VMs you will run. For open source and trial OS VMs, this could be free. For Windows Server VMs, you would need to purchase one or more Windows Server 2012 Standard or Data Center Edition licenses (depending on how many CPU sockets the server has and how many Windows Server VMs you want to run). Each Standard Edition license lets you run 2 Windows Server VMs. You could purchase multiple licenses if you need more VMs. Or you could purchase Data Center edition, which will let you run an unlimited number of Windows Server VMs. Windows client OSs need a different type of license. More details here: http://www.aidanfinn.com/2013/09/windows-server-2012-r2-licensing/

Remember that a license is a legal agreement between you and Microsoft.  I doubt that your lawyers or auditors would accept random responses from a technical forum as testimony that would stand up in court.  Hindy provided a good link to a document provided by Microsoft that should help you understand things.  You should also contact a trained Microsoft licensing specialist.  You can find those are the reseller from whom you purchase your Microsoft software or from Microsoft itself.