In essence, Netlify CMS is an open-source React app that acts as a wrapper for the Git workflow, using the GitHub API. This allows collaborators to create, edit, review, and publish content without writing code or dealing with version control, and it allows developers to manage this content with familiar build tools and the convenience of Git.
For a more thorough introduction, check out this talk my Mathias Biilmann at the JAMstackSF meetup:
Now that you’re interested, why not try it out? Here are some links to get you started: