Bindings are not only the way to attach yourself to your skis, but they are an important piece of safety equipment as well. They keep you in your skis when you need to locked in, and release you when the appropriate amount of force is applied to let you out to prevent injury. Since they are safety equipment they should only be mounted, adjusted, and tested by certified technicians. It is strongly discouraged by skis.com, and the manufactures that you make any adjustments to your bindings yourself, no matter how minor they seem to be.
Downhill bindings have a standard fixed toe and heel, and are the majority of what skis.com sells. They are calibrated and manufactured with safety and performance in mind.
Alpine Touring bindings are designed to hike or skin up the mountain and ski down. The heel piece releases off of the ski, while the toe remains fixed to the ski, for making your way up to freshies. This category includes bindings that are designated as sidecountry/backcountry that work as well as downhill bindings, but allow you to skin.
Race bindings maintain a narrow platform due to the fact that race skis are still narrow in the waist. They typically use more metal components for additional durability, and have higher DIN ranges to accommodate higher speeds.
Binding Brakes are replacement brakes in case you have bent or broken yours. They allow you to only replace the brakes if you change ski widths.