How to call standard gem commands not through the terminal, but in the program code?

Question

ruby

This means the script is executed and along the way it offers to install the gem

Answer 1

system("gem install rails")
For example, but to do so, I would not advise.
You are trying to use some kind of gem, if not, inform the user about it, let him install it. Putting modules for him is not ice, to put it mildly.

Answer 2

You read at least the basics. Read at least one book and read online resources.
On the topic, you include the gem in the same way as in the terminal, first require 'gem_name'
Then work with it like GemName::Class.method, or Class.new, you can include all the methods in your file using the include method directly in your class.