Why Should I use GatsybyJS?
It’s a static site generator that uses React. So in other words it offers all the benefits of React Server-Side Rendering, without a server.
You could you any other site generator, like Hugo or Jekyll, but they don’t offer any React features, like code splitting, lazy loading, service worker, etc.
For example https://reactjs.org/ is built using Gatsby.js
Perhaps you could give more context, like what sort of things you want to accomplish, why you’re considering site generators in the first place, and why you’re not considering other, similar technologies?
Thank you for your answer. How can I start with GatsbyJS?
Try the tutorial https://www.gatsbyjs.org/tutorial/