External resources
Here is a collection of learning material that can help you get familiar and master the language.
Language Introduction
This course is targeted at novice Crystal programmers and conveys a basic understanding of the language’s core concepts. Prior programming experience is recommended, but not required. This course can help you learn your first programming language.
Tutorial: Language Introduction
Crystal Programming
Crystal Programming is a project-based book by George Dietrich and Guilherme Bernal. It covers all the fundamental concepts needed to start programming in Crystal such as OOP and concurrent programming.
Crystal for Rubyists
If you know Ruby, you are just a few steps from learning Crystal. From Core Team Member and Kemal creator Serdar Dogruyol comes this guide that will help you to transition from Ruby to Crystal.
Exercism
Get your hands on Crystal with a series of exercises, and compare your solution to that of the many members who tried already.
CodeCrafters
Keep your Crystal skills sharp by learning how to build real things. Practice interesting programming challenges like building your own Git, Redis, Docker, and even SQLite from scratch.
Registration to CodeCrafters is free. With the link above you can get a 40% discount when upgrading to an annual paid plan.
If you opt to pay, 60% of the income will come back to the Crystal team to help developing Crystal!