clay bars are sold from several different manufactuars, but imho along with most other car detailing supplies meguiars is the only way to go.
when i clay what i do, is wash/debug/de-tar the Jeep, don't dry it yet, usung the supplied meguiars spray, in small areas you take the clay bar and slide it over the area you are cleaning, the idea is to remove the small particles that are inbeded within the top coats of clear coat and wax that's present, rub your hand over the vehicle before you do this and then after you will notice a huge difference. once you do an area you kneed the clay bar to get a clean surface to work with again, and then do another section of your jeep keep doing this process over and over till your done with the jeep. you can usually get two times out of one clay bar, i do anyway. btw if you drop the clay bar on the ground, say by by and go buy another one.