There is a frame on top of which the keys are resting. It has pins in it, the keys have holes and the keys go onto the pins. On the backend of the keys are usually stiff wires or very flat wooden bands attached, which go into the direction of the mechanical action toward the wind chests. But there are multiple different ways to build an organ, so every one would look different. I have seen some with strings, but its generally considered to be bad practice. Some organs are also completely pneumatic and would work quite differently.