In this video, Adam shows you how you can use the Power BI REST APIs to get an embed token. This is done with the GenerateToken API. In order to do this, you have to register an app with Azure Active Directory, then you need to write some code to authenticate with Azure Active Directory (Access Token) and then make the Power BI REST API call to generate the embed token.
If you are developing an application, and want to embed your dashboards, tiles or reports within your application, then this will help you!