Responsive Web Design... where do I start?

So, I've been wanting to redesign for mobile users. I currently have designed for fixed width (960px) and realize it absolutely the wrong choice. I am no CSS expert, but have never dealt with using percentages for my design, which I assume I'll need to do if I'm going to build a "responsive" website design (wasn't it once called "fluid" or I guess that's a bit different).

However, I'm not worried about using percentages over fixed values. That's easy. What I want to understand is if there is a way to detect a user on a mobile browser and give them a slightly different experience. For example, hiding the left navigation bar and enabling it to show up when a new icon (that only appears for mobile users) is clicked. Or telling the browser to zoom on only the content when someone tap zooms.

I understand the concepts of "fluid" design where you can user percentages to have everything scale down. However, there are definitely mobile-specific tricks I'd assume and I just don't know where to start...

Can someone help me out here? Any and all help greatly appreciated. Thanks!