Windows Server 2012 R2 CALs

I am upgrading a Dell PowerEdge T310 server from Windows Server 2008 to Windows Server 2012 R2.

I found a good deal online $132.82

My question is about Client Access Licenses (CALs)

What is the process of acquiring CALs? After I install the new operating system what are my steps to ensure that my 2 local users will be able to connect to the server?

How much are CALs?

Thanks