As you know Oracle Data Guard provides high availability, data protection, and disaster recovery. It provides a comprehensive set of services that create, maintain, manage, and monitor one or more standby databases.
If you begin working with Data Guard and you want to learn quickly, I would like to mention a book around this area that I just finished to review:
Oracle Data Guard 11gR2 Administration Beginner’s Guide
This book has been written by Emre Baransel and Nassyam Basha.
From my point of view this is a very good book to start around this subject. It is easy to read and provides also useful real-word practices and issues.
1: Getting Started Chapter
2: Configuring the Oracle Data Guard Physical Standby Database Chapter
3: Configuring Oracle Data Guard Logical Standby Database Chapter
4: Oracle Data Guard Broker Chapter
5: Data Guard Protection Modes Chapter
6: Data Guard Role Transitions Chapter
7: Active Data Guard, Snapshot Standby, and Advanced Techniques Chapter
8: Integrating Data Guard with the Complete Oracle Environment Chapter
9: Data Guard Configuration Patching Chapter
10: Common Data Guard Issues Chapter
11: Data Guard Best Practices Pop Quiz Answers
You can find some sample chapters here or the whole book here.