Most likely you have homebrew installed on your machine, if not follow these instructions.
To install Exercism CLI, type the following on your terminal:
brew update && brew install exercism
To make sure it was installed correctly, run:
exercism --version
Now let's configure Exercism CLI with you api key. This link will take you to your account on exercism.io. If you do not have an account yet, just sign in with your Github credentials. Copy your api key and run the following on your terminal:
exercism configure --key=YOUR_API_KEY
You should be ready to fetch an exercism now.
To download a challenge, run the following on your terminal with your language of choice:
exercism fetch <language>
(For exmaple, Ruby: "exercism fetch ruby", JS: "exercism fetch javascript" etc.)