Once you've chosen the appropriate section, functions are clearly labelled to choose from. Just click on the keybinding you want to change, and press the appropriate keys you want the function bound to -- the same as it functions right now. There aren't really any major changes in regards to the keys you can bind, it's the same list. The layout has simply been refined and rearranged into something that is much easier to look at, and easier to use.
Given the customization capabilities of so many addons out there, this new layout may not be of use to everyone. But if you, like me, are sick of scrolling through a seemingly endless list of options in one small panel in order to keybind one function, your days of being irritated are almost over.