Vickie, they are usually just a "friction fit". There are tabs on the inside that when the beauty/trim ring is pressed into the wheel, they compress and hold the ring on. Those tabs can scratch the paint
though, so watch for that if you don't want to damage the paint
on your wheels and if you are not certain that you want that look; if you take them off you may have small scratches. Not a problem if you leave them on of course.
The rings can be found ranging from chromed plastic to polished stainless.
I think the rings would complement the chrome nuts and bearing covers very nicely!
Looking forward to more pics!