You can read more about using Postman with basic authentication on Microsoft Docs at https://docs.microsoft.com/en-us/dynamics365/business-central/dev-itpro/developer/devenv-develop-connect-apps#exploring-the-apis-with-postman-and-basic-authentication.
Postman is a very robust product used for API development. There's a very good collection of documents with additional information on all of its features available at https://learning.getpostman.com.