How do I run ruby code using the shell?

Hello,

I am doing the Alpha Curriculum and successfully installed everything. However, in the second section the course gives code and tell you to try defining and invoking a method in the shell. How do this? Little confused as to what the shell is and how to access based on the environment set up done previously for the alpha curriculum.

Type irb in the terminal to access the ruby shell

Awesome thanks for all the help!