you need to modify the splitter to fit.
about 5 mins with a sharp knife.
then offer it up to bumper, and either drill and srew it to underside of the bumper or use self tapers.
personally i made a small pilot hole as wanted to avoid possibility of cracking the bumper.
what does it do?
well not alot.
in motorsport its an aero dynamic thing to
help keep the front end planted.
in this case they are more of a add on to give a more sporty look.