This week's book giveaway is in the OO, Patterns, UML and Refactoring forum. We're giving away four copies of Refactoring for Software Design Smells: Managing Technical Debt and have Girish Suryanarayana, Ganesh Samarthyam & Tushar Sharma on-line! See this thread for details.
At the heart of understanding Spring Framework are the concepts of beans, DI, Spring IoC container and AOP. So, you should focus on DI, bean lifecycle, how Spring IoC container modifies bean definitions and bean instances, and Spring AOP framework.