Postman (https://www.getpostman.com/) is a popular tool for testing out a web api. Figuring out how to use it with a resource protected by Azure AD is a bit daunting for many. I created this walkthrough video to help you understand how to use the postman oauth 2 authorization helper with AAD.
Here are the values I use in the video so you can copy/paste them:
Auth URL: https://login.windows.net/common/oauth2/authorize?resource=https%3A%2F%2Fb2byour.resource.domain%2F
Access Token URL: https://login.microsoftonline.com/common/oauth2/token