Create basic gem example
$ mkdir basic_gem
$ cd basic_gem
$ touch basic_gem.gemspec
$ vi basic_gem.gemspec
then you can fill ref: https://guides.rubygems.org/specification-reference/
see lib/basic_gem.rb
Then you can generate gem gem build basic_gem.gemspec
Then should show successful meesage
Successfully installed basic_gem-0.1.0
Parsing documentation for basic_gem-0.1.0
Installing ri documentation for basic_gem-0.1.0
Done installing documentation for basic_gem after 0 seconds
1 gem installed
Then you can install gem install basic_gem
(uninstall gem uninstall basic_gem).
in irb you can test
$ irb
> require 'basic_gem'
> BasicGem::WhoIs.hello