What are the essential and important steps to license Windows Server 2008 R2 on physical machine ? how many are types of licensing and what are best?

Depends up on the requirement, we will opt the licensing options from microsoft. There have n number of options like Volume Licensing for Physical/Virtual, OEM, etc.  Basic server license is shortly described below

Windows Server is primarily licensed using a Server + CAL model or a Processor + CAL model. Windows Server Standard and Enterprise editions are licensed using the Server + CAL model, while Windows Server Datacenter and Windows Server for Itanium-Based Systems editions are licensed using the processor + CAL model. Under both models, the CAL that accesses the instance of Windows Server must be equivalent or higher in version than the server being accessed

Each license cover2 physical processor .

You should have internet connection and valid license key to activate windows2008 and regarding for license type it depends on your needs you can install standard edition, enterprise edition, web edition, or data center edition.

Here is the complete guide regarding licensing of Windows Server2012 R2:

http://www.microsoft.com/licensing/about-licensing/windowsserver2012-r2.aspx

And there are4 types of licensing which are as follows, usually based on CUP's further details you can have from above link, the best is Datacenter but it hit  you a cost too but you have have unlimited MS HyperV VM's and in Standard Edition you can only create2 or i think4 may be.

Foundation

Essential

Standard

DataCenter

Dear Hayat, I don't think there is much steps in this, you only need to insert the license key during of after the installation of the O.S

about the types i think there are no much types, there is only physical and virtual O.S, and Number of servers, that depends on How may number of Servers you want deploy the license in.