Setting up your app domain configuration for SharePoint 2013 may be little complex for the beginners and soon end up with mess.
I really found the easiest step by step explanation by Mirjam, SharePoint Server MVP.
She explained on how to create the DNS and forward lookup zone to host your apps in separated App Domain.
I strongly recommend not to rely on other sources including MSDN site, if you are a starter.
Visit the Mirjam's post's on how to configure app development on your server or local development.
http://sharepointchick.com/archive/2012/07/29/setting-up-your-app-domain-for-sharepoint-2013.aspx