Read that link QWERT posted above for more info on the more traditional BUD LNB, scaler ring, and servo motor for polarity.
The BUDs of 20 years ago used one expensive LNB, on one polarity, and a servo motor to change that polarity from V to H.
That technology is still fine today, as it is well proven and reliable.
Voltage-controlled LNBs use 12/18 volts to change between vertical and horizontal polarity.
The bulk of modern FTA receivers only have the ability to control polarity through the voltage fed to the LNB.
For examples of that sort of hardware, read the link I posted above for Linuxman aligning his GeoSat on C & Ku.
There is a lot of fundamental technology to learn, but once you have a grip on it, mostly it's pretty simple.