Creating Gem file

rails new project_name -T

Installation

# install specific version
gem install fog -v 1.8

# unintall gem
gem uninstall fog

Gem Package Grouping

# requiring globally
gem 'rails', '~> 6.1.4'

# grouping as a command
group :test do
  gem 'capybara', '~> 2.3.0'
end