25-8-2016: Update because the UI to create a Service in VSTS changed
When you want to access Azure from VSTS there are multiple possibilities. It’s for example possible in VSTS to configure an Azure Classic Endpoint and after that configure the endpoint with credentials or with a certificate. The ARM way is to add an Azure Resource Manager Endpoint. To configure this you will need the settings of an Azure Service Principal. This blogpost tells you how to create both the Service Principal in Azure and the ARM Endpoint in VSTS.