I assume you have already downloaded and installed Ruby. Here’s what you need to do next:

1. Run gem install jekyll bundler.
2. Copy the theme in your desired folder.
3. Enter into the folder by executing cd name-of-the-folder.
4. Run bundle install.
5. If you want to access and customize the theme, use bundle exec jekyll serve. This way it will be accessible on http://localhost:4000.
6. Upload the content of the compiled _site folder on your host server.