Assist default sentences: add section explaining how ... (#27242)

* Assist default sentences: add section explaining how to view supported sentences

* fix typo

source/docs/assist/builtin_sentences.markdown

@@ -25,3 +25,36 @@ In addition to individual entities, commands can target **areas**:
 Entity [aliases](/docs/assist/aliases) are also matched so multiple names can be used, even in different languages.
 
 You can extend the built-in sentences or [add your own](/docs/assist/custom_sentences) to trigger any action in Home Assistant.
+
+## View existing sentences
+
+Broadly speaking, you can use your voice to turn things on or off, inquire about a state, or change the brightness or color of a light.
+
+If the voice assistant doesn't understand you, you may need to rephrase your sentence a bit.
+To get an idea of the specific sentences that are supported for your language, you can do the following:
+
+1. Take a look at the test sentences:
+    * On github, in the [tests](https://github.com/home-assistant/intents/tree/main/sentences) folder, open the subfolder for your language.
+    * Look through the test files to see the example sentences that have been tested.
+    * The second part of the file name shows the intent, the first part shows the domain. For some domains, such as covers, fans, and light, there are specific sentences.
+        The other domains are covered by the generic *homeassistant_*.
+
+        ![Example of a folder of assistant sentence test files](/images/assist/intents-test-files.png)
+        
+    * The screenshot below shows sentences used to test the command to turn on the lights. Note that *Living room* here is just a place holder. 
+        It could be any area that you have in your home. 
+
+        ![Example of a set of test sentences](/images/assist/assist-test-file-light-turn-on.png)
+
+2. View the sentence definition:
+    * On github, in the [tests](https://github.com/home-assistant/intents/tree/main/tests) folder, open the subfolder for your language.
+    * Open the file of interest.
+
+        ![Sentences definition for turning on the light](/images/assist/assist-sentence-definition-01.png) 
+
+        * () mean alternative elements.
+        * [] mean optional elements.
+        * <> mean an expansion rule. The view these rules, search for `expansion_rules` in the [_common.yaml](https://github.com/home-assistant/intents/blob/main/sentences/en/_common.yaml)   file.
+        * The syntax is explained in detail in the [template sentence syntax documentation](https://developers.home-assistant.io/docs/voice/intent-recognition/template-sentence-syntax).
+
+