There are a number of helpful online resources for learning to use Xcode and for Cocoa development in general. A few author favorites are listed here.
This book’s companion site (http://xcodebook.com) contains Xcode 4 news, tips and tricks, downloadable sample projects reflecting each chapter’s tasks, and errata.
Developer Forums (http://devforums.apple.com)
Apple’s developer forums site has an Xcode-specific forum with a number of active members. A current Apple Developer account is required.
Xcode-Users Mailing List (http://lists.apple.com/mailman/listinfo/xcode-users)
The Xcode-Users mailing list doesn’t require an Apple Developer account to use and is an active list full of helpful ...