Exhaust tips function in two ways. First, the most apparent, they add a bit of style and uniqueness to the tail end of your car. Looking at a shiny exhaust tip on your Legend is certainly more appealing then the rusty old thing from the factory. It's a lot more classy and elegant. The other function of the exhaust tip is it can actually affect the volume of your exhaust tone. The larger the exhaust tip, the more volume you'll get from it. Usually anything greater than 3½" will make your exhaust noise louder than it normally is without one. Keep in mind that an exhaust tip only works effectively with an aftermarket performance muffler. If you have the stock muffler or a quiet aftermarket one, the exhaust tip will only slightly change the tone because there won't be any noise to change.
Exhaust tips come in many types, styles, and sizes. Tips are either resonated or non-resonated. Non-resonated tips are just plain stainless steel tips. The resonated tips are lined with fiberglass to dampen the exhaust noise a little further. Sizes (diameter measurements) range from 2 inches to 5 inches wide. As for styles, there are many to choose from. There's round, oval, square, slashed, etc. These tips will either be welded on, or if possible, clamped on.
You have to be careful having any exhaust tip over 3 inches nowadays in California because lately law enforcement have been trying to crack down on vehicles with "modified exhausts". A modified exhaust is simply any exhaust that is louder than 92 db, which constitutes disturbing the peace. Most aftermarket exhausts don't break the sound ordinance, but usually police don't even listen to your exhaust noise. They just pull you over once they spot a large exhaust tip sticking out the rear of your car. B.S.