Cactus is a modern build tool that runs on Python and uses Django's templating engine. To use Cactus, you need to install it using pip and create a virtual environment. Once installed, you can create a new site with Cactus by running `cactus create` followed by the name of your site. You then need to prepare your site for deployment by creating a `.gitignore` file and a `requirements.txt` file, which lists the dependencies required by your project. After that, you can push your site to GitHub and link it to Netlify, where you can configure settings such as the build command and choose which repository to deploy from. Once configured, Netlify will build and optimize your site, making it live and available to the public.