docs(v2): plugins (#1629)

website/docs/using-plugins.md

@@ -3,9 +3,61 @@ id: using-plugins
 title: Using Plugins
 ---
 
-TODO: Give a high-level overview about plugins and what they can be used for.
+<!-- A plugin is a package that exports a class which can be instantiated with configurable options (provided by the user) and its various lifecycle methods will be invoked by the Docusaurus runtime. -->
 
-#### References
+Plugins are the building blocks for Docusaurus 2 sites' features. Each plugin handles its own individual feature. Plugins may work together as [presets](./presets.md).
 
-- https://v1.vuepress.vuejs.org/plugin/
-- https://www.gatsbyjs.org/docs/plugins/
+Docusaurus 2 provides a few essential plugins such as [sitemap](#docusaurus-plugin-content-sitemap), [analytics](#docusaurus-plugin-content-analytics). And you may write your own plugins for customized features.
+
+In this doc, we talk about how to use plugins with Docusaurus' official plugins. To learn about the design implementation and how to write your own plugins, check out [Advanced Guides: Plugins](./plugins.md). For API reference, check out [API Reference: Plugins]('./plugins-api.md).
+
+## Using plugins
+
+To use a plugin, add the plugin to the `plugins` field of your `docusaurus.config.js`.
+
+For some plugins, providing just the plugin name is sufficient. For plugins that require options, specify the plugin in a `['plugin-name', options]` array.
+
+```js
+// docusaurus.config.js
+module.exports = {
+  plugins: [
+    '@docusaurus/plugin-google-analytics',
+    ['@docusaurus/plugin-sitemap', opts.sitemap],
+  ],
+};
+```
+
+## Passing options to Docusaurus plugins
+
+Docusaurus' classic template is scaffolded with the classic preset, which in turn includes the following official plugins. You may read more about the configurations of these plugins in our [Advanced Guides: Plugins](./plugins.md).
+
+- `@docusaurus/plugin-content-blog`
+- `@docusaurus/plugin-content-docs`
+- `@docusaurus/plugin-content-pages`
+- `@docusaurus/plugin-content-analytics`
+- `@docusaurus/plugin-content-gtag`
+- `@docusaurus/plugin-content-sitemap`
+
+If you initialized your site using the classic template, you do not have to specify them individually in your `docusaurus.config.js`. To provide the neccesary fields to certain plugins, i.e. `trackingID` of `@docusaurus/plugin-content-analytics`, pass them in the preset field.
+
+```js
+// docusaurus.config.js
+module.exports = {
+  presets: [
+    [
+      '@docusaurus/preset-classic',
+      {
+        docs: {
+          sidebarPath: require.resolve('./sidebars.js'),
+        },
+        theme: {
+          customCss: require.resolve('./src/css/custom.css'),
+        },
+        googleAnalytics: {
+          trackingID: 'UA-000000-2',
+        },
+      },
+    ],
+  ],
+};
+```