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The add fields method helps developers specify fields for the standard controller to query in Visualforce pages. public AccountController(ApexPages.StandardController stdController){             this.controller = stdController;             List<String> fieldNamesList = new List<String>{Type,Industry};             stdController.addFields( fieldNamesList );             // stdController.addFields(new List<String>{'Name', 'TaxExemption__c', ' Industry '}); } Reference: https://developer.salesforce.com/docs/atlas.en-us.pages.meta/pages/apex_ApexPages_StandardController_addFields.htm

To display a page message on a Visualforce page, you can use the <apex:pageMessages> component. This component is typically used to display messages to users, such as validation errors, informational messages, or confirmation messages. Here's how you can use it: <apex:page controller="YourControllerName">     <!-- Your Visualforce page content goes here -->          <!-- Page messages section -->     <apex:pageMessages /> </apex:page> Within your Apex controller or controller extension, you can add messages to be displayed using the Apex addError() method. For example: public class YourControllerName {     public PageReference yourActionMethod() {         // Perform some action                  // Add a message         ApexPages.addMessage(new ApexPages.Message(ApexPages.Severity.INFO, 'Your message here.')); ...