If you have Windows Server licences with Software Assurance then you have the Azure Hybrid Use Benefit. This means that you can choose to use your licences to license the Windows Server part of an Azure virtual machine and so just pay for the compute cost of the VM.
If you have an EA you can deploy VMs from specific Marketplace images that are pre-configured with the Azure Hybrid Use Benefit. Without an EA you can upload a custom VM and deploy using a Resource Manager template or Azure PowerShell.
This article explains all and has some useful illustrations http://bit.ly/2lbjIbe.