Sometimes the best way to get started with an API is to actually call it.
Tryapis gives you a Postman-like interface for popular REST APIs, with built-in documentation based on the API's latest Swagger spec.
For example, check out Spotify's API: https://tryapis.com/spotify
Currently supported APIs: GitHub, Slack, Spotify, Netlify, GCal, GSheets, Drive, Gmail, GMaps, Twitter
Let me know if there are any others you'd like added! I'll also open source the project if there's interest :)