To be honest no book in the world will make you fully grasp design patterns until you've written an application or a system from top to bottom, hitting the problems and changes that are hard to fix, and then use a pattern to accomodate for these problems and changes successfully.
I'm saying this even though I whole heartedly recommend the Heads First into Design Patterns book.
For a complete novice or a beginner it is difficult to describe design patterns because you probably haven't "lived through" the problems they're trying to solve and even reject implementing patterns that would make life harder for other programmers.
Implementing a pattern is one thing, doing so successfully in something that is already in production and your boss/comrades is yelling at you is another. Being able to fix legacy systems with refactorings (Refactor to Patterns is an excellent resource) is a skill that takes time to master.
You'll learn. Just be patient, it'll take time to let it sink in. I'm pretty sure you're like me when I started learning them, there is a lot of head scratching involved. It will take several years of programming practice to get it right and get the actual a-ha moments. At least it did for me.
But until then just make stuff up during the interview... or be honest about it, just mentioning that you've read them and trying to grasp is enough for most. Just don't mention the Singleton pattern and how much you love it in a TDD shop.