Application logic is often provided as an API instead of via an interface usable by end users. API Management can help with marketing an API. Provisioned APIs can be assigned permissions, supplemented by converting input and output values, and supplied with product-specific SLAs. The usage of APIs can be monitored, evaluated, and billed accordingly as necessary. The provisioned API can be operated on Azure or externally.
API Management Learning Path
Azure API Management 101
Azure API Management Dive Deep
Getting Started with Azure API Management REST API
Azure API Management and the API Economy