They have self tapping screws along the underside, and two at either end inside the arches, and use a combination of foam adhesive tape on the inner edges and pop clips that locate in plastic inserts along the sill of the bodywork not hard to fit to a non aero car with some sikaflex If they will be permanent
Easiest way to remove them without damaging anything is to undo all the fixings and grab the front top edge of the end caps, slowly and carefully prise it away whilst heating the bodywork edges carefully with a hairdryer, this softens the glue and let's you gradually pull the skirt off without it cracking or bending. The main body of the skirts will come away with a well placed tug to release the pop clips and repeat the hairdryer/pull trick on the back part that is stuck to the body