Instructions are provided below about how a golpeador should be attached to a guitar soundboard. I would like to thank my neighbor and friend of many years Sascha Nowak, who taught me with a lot of patience how to attach a golpeador professionally. He is also shown in the pictures here. He is a real artist and one of the best guitar builders I know.
The golpeador protects the soundboard against taps, which are required when you play using flamenco technique, and scratches. Shellac-polished soundboards are especially sensitive and consequently need to be protected, but lacquer cannot withstand the continual tapping (golpes) on the soundboard without visible traces either. 

You first have to take off the strings (you can leave them attached at the bridge). Then you have to clean the soundboard and ensure that it is free of grease. Careful with shellac! Do not use any solvents containing alcohol; otherwise the shellac can be dissolved. Then take a golpeador and check on which side the thin protective foil is, which protects the glue. To do this, simply pull on one corner with your thumb; then you can see immediately on which side the thin protective foil separates. This side should be placed face down. On the upper side, mark the side that will be adjacent to the bridge using a felt pen, the markings of which can be wiped off again. If we mix up the sides, the cutout for the sound hole will not be in the right place.