Check your development environment! You'll need Node.js, the Gatsby CLI and node-gyp installed. The official Gatsby website also lists two articles regarding this topic:
npm install
gatsby develop
You can add other features by having a look at the official plugins page.
gatby build
This site is built with GatsbyJS using the gatsby-universal template. This decision was made to get something oof the ground quickly
The CSS is power through a combination styled-components, the global.css file, and inline JSX (for global overrides).
Copy the content of the public folder to your webhost or use a website like Netlify which automates that for you.