The Netlify Build Plugins series has reached its third part, where publishing and sharing plugins are covered. To publish a plugin, developers must first create a package.json file with specific requirements, including a name that starts with "netlify-plugin-", keywords containing "netlify" and "netlify-plugin", and repository and bugs fields set to the plugin's repo and issues path respectively. Developers can then push the plugin to npm using `npm login` and `npm publish`, updating the version before each new release. Once published, plugins are listed on the Build Plugins repo, where they can be cloned or forked and added to the `plugins.json` file with author information, description, name, package, repository, and version fields. The final step is to push code up and make a pull request for review, after which the plugin is added to the master list and can be shared within the community.