Homebrew PCBs

Ok. I admit I'm ignorant when it comes to this subject. How is an IC lead connected to say layer 8 on a 16 layer PCB. I'm only using this as an example. The same thing with connecting to layer 2 of a four layer PCB. The top and bottom layers are straight forward. A 16 layer board is built one layer at a time (etching)? I have never worked with anythng other than 2 layer PCBs as far as installing/removing components. Modern computers use multilayer PCBs. Any guidance would be appreciated. TIA  Charles  AE5EW