Apex REST Callouts

Authorize the endpoint URL of the callout:

1. From Setup, enter Remote Site Settings in the Quick Find box, then click Remote Site Settings.

2. Click New Remote Site.

3. For the remote site name, enter animals_http.

4. For the remote site URL, enter the endpoint url.

5. Enter the description

6. Click Save .

Check the following for implementation of the call out -https://github.com/JohnsonTitus/apxWebSrvCallOut.git.

It shows how to parse JSON or XML response.

To test a callout follow the following link - https://trailhead.salesforce.com/en/content/learn/modules/apex_integration_services/apex_integration_rest_callouts

https://developer.salesforce.com/docs/atlas.en-us.apexcode.meta/apexcode/apex_classes_restful_http_testing_httpcalloutmock.htm

Another Eg: