I am going to explain here a way to add a breadcrumb in the default Magento Contact Us Page as an example
1) Create a layout file
I have a theme module Decryptweb_Project, so creating a layout file inside it
app/design/frontend/Decryptweb/Project/Magento_Contact/layout/contact_index_index.xml
2) Reference the existing breadcrumbs block
<?xml version="1.0"?> <page xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" layout="1column" xsi:noNamespaceSchemaLocation="urn:magento:framework:View/Layout/etc/page_configuration.xsd"> <body> <referenceBlock name="breadcrumbs"> <action method="addCrumb"> <argument name="crumbName" xsi:type="string" translate="true">Home</argument> <argument name="crumbInfo" xsi:type="array"> <item name="title" xsi:type="string" translate="true">Home</item> <item name="label" xsi:type="string" translate="true">Home</item> <item name="link" xsi:type="string">{{baseUrl}}</item> </argument> </action> <action method="addCrumb"> <argument name="crumbName" xsi:type="string" translate="true">Contact Us</argument> <argument name="crumbInfo" xsi:type="array"> <item name="title" xsi:type="string" translate="true">Contact Us</item> <item name="label" xsi:type="string" translate="true">Contact Us</item> </argument> </action> </referenceBlock> </body> </page>