Clarify API usage

site/docs-md/apis/index.md

@@ -13,4 +13,39 @@ Capacitor includes a number of Native APIs that are available to all Capacitor a
 
 For those coming from Cordova, the core Capacitor APIs cover much of the core Cordova plugins, and also include some new ones.
 
-See the APIs list on the left menu for the full list of available APIs.
+See the APIs list on the left menu for the full list of available APIs.
+
+## API Usage
+
+To use a Capacitor API, follow these steps:
+
+1) Import the `Plugins` object. It represents the registry of all Capacitor plugins.
+```typescript
+import { Plugins } from '@capacitor/core';
+```
+
+2) Get a plugin from the Plugin Registry (`Plugins` object).
+```typescript
+const { Browser } = Plugins;
+```
+
+3) Use the plugin API:
+```typescript
+async openBrowser() {
+  // On iOS, for example, open the URL in SFSafariViewController (the in-app browser)
+  await Browser.open({ url: "https://ionicframework.com" });
+}
+```
+
+A common mistake is to import a plugin directly, then use the plugin API immediately, resulting in the web implementation being used:
+```typescript
+import { Browser } from '@capacitor/core';
+
+async openBrowser() {
+  // On iOS, for example, this will open the URL in Safari instead of 
+  // the SFSafariViewController (in-app browser)
+  await Browser.open({ url: "https://ionicframework.com" });
+}
+```
+
+By using the plugins from the plugin registry (`Plugins` object), the native implementation of the plugin is used (if available), with fallback to the web version.