How and where do they add parts to the crane to get it higher in order to make taller buildings?

I've always been puzzled how cranes operate.Because as buildings get taller so do cranes but i don't know how they increase the height of the cranes.Can you help answer this please?

search for others, animation and video of process more edit Some cranes actually climb the structure of the building and are taken apart when the building reaches its full height.