This course is to teach concepts of cybersecurity with ruby on rails as an example. You can apply the concepts learned here to any language of your choice with a change in syntax and a bit of code-wise implementation.
Having said that, the following resources will help you gain a good understanding of ruby on rails and cybersecurity.
If you know the following, you're good to go!
You can read the introduction page. If you are curious and want to learn more about RoR, then proceed to learn the whole tutorial to RoR.
Getting Started with Rails - Ruby on Rails Guides
Read the whole article. It's very useful and will help you build a sample application in rails to get to know how it all works. It is not compulsory but it will be an added advantage if you know how to build something before you go ahead and try to secure it.
Ruby on Rails Tutorial | A Complete Guide To Ruby On Rails - HKR
An easier guide to follow with to-the-point instructions. You can quickly get up to speed on RoR using this tutorial.
This is a sample rails application. You can learn how to start rails servers and see the logs here. The steps are very clear and will guide you on how to start a rails application.
For those of you who like to read books, this is a good place to start.