Environment variables are like boxes that hold information that can't be uploaded to Github. As a result, you do not have to write the password directly in the application. By passing data from the OS, you can run the application without worrying about information leakage.
$ bundle install
In the root directory where the Gemfile is located Create an .env file
KEY='*******' #Enter the key and password you want to use SECRET_KEY='*******'
You can call it.
If you forget this, information will be leaked, so be sure to set it.