The guide on using APIs with Ruby on Rails provides a comprehensive tutorial for beginners on how to integrate APIs into Rails applications, specifically focusing on building a simple travel planner app. The article explains the concept of APIs, particularly RESTful APIs, and details the process of connecting to an API using Ruby, highlighting the advantages of Ruby's readable code when compared to other languages like Node.js. It covers the basic steps such as creating a new Rails app, setting up the initial view, fetching data from APIs, and displaying results, using examples like the REST Countries API and the Open Weather Map API. The tutorial also emphasizes the importance of understanding HTTP request methods and provides practical insights into using the RapidAPI platform for testing various APIs. Additionally, it encourages readers to expand their skills by experimenting with additional APIs, suggesting further integration with services like the SkyScanner API to enhance the travel planner app's functionality.