A: System Center 2012 provides several ways to provision a virtual machine (VM) through System Center Virtual Machine Manager (SCVMM). One way is to use the SCVMM self-service portal; however, the SCVMM out-of-the-box web portal is very basic and doesn't offer much more than the out-of-the-box self-service portal provided with SCVMM 2008 R2.
Much better options are available in System Center 2012 (remember that with System Center 2012 all of the System Center product is available including App Controller and Service Manager).
The next option is to use System Center App Controller, which offers a rich Microsoft Silverlight experience to deploy VMs and even entire services. After it's deployed, App Controller also provides management capabilities of the VMs and services deployed (see screen shot below).
Service Manager enables a full Service Catalog that can offer users not just VM provisioning but also assistance with application requests, incidents, problems and really anything else that can be defined as an offering, plus rich workflows and authorizations. I advise you to use Service Manager's Service Catalog and web portal as the primary method to request VMs, then use App Controller to actual manage and interact with VMs.
I made a video that explains provisioning more.