CEXT-4373: Update the oope shipping methods documentation

Author: oshmyheliuk

src/pages/starter-kit/checkout/getting-started.md

@@ -29,6 +29,8 @@ You must install or have access to the following prerequisites to develop with t
 
 ## Install Commerce modules
 
+Before installing modules ensure that you have the required credentials in your `auth.json` with [access to the Adobe Commerce repository](https://experienceleague.adobe.com/en/docs/commerce-operations/installation-guide/prerequisites/authentication-keys).
+
 - Install the Out-of-Process Payment Extensions (OOPE) module on Adobe Commerce
 
     To enable out-of-process payment methods in Commerce, install the `magento/module-out-of-process-payment-methods`. This module enables out-of-process payment functionalities.

src/pages/starter-kit/checkout/use-cases.md

@@ -211,7 +211,9 @@ You can find examples of how to filter out payment methods using customer data o
 
 ## Shipping methods
 
-You can add shipping methods to the checkout process by using [webhooks](../../webhooks/index.md).
+You can add shipping methods to the checkout process by using [webhooks](../../webhooks/index.md). 
+
+To be able to add shipping methods, you must first [run a script to automatically create shipping carriers](./configure.md#create-shipping-carriers) or [to create shipping carriers manually](./shipping-reference.md#shipping-api-reference) using REST Api. Only shipping methods with the registered carriers for them will be available in the checkout process.
 
 After the webhook is registered, every time a shopping cart is requested, a synchronous call is dispatched to the App Builder application implementing the shipping method to calculate the shipping cost and provide the available shipping methods.