Use Postman with Web API
There are number of third-party request composer tools that allow you to authenticate to Dynamics 365 for Customer Engagement apps instances, compose Web API requests, send them, and view responses. Postman is one of the most popular.
Use Postman to try ad-hoc queries or verify the behavior of operations without writing a program. This section covers information on how to configure a Postman environment that connects to your Dynamics 365 for Customer Engagement apps instance and use Postman to perform operations with Web API.
Postman offers many other capabilities beyond those covered in this content. More information: First 5 things to try if you’re new to Postman