here you go
auto detailing clay bars use for cleaning the paint which shampoo alone fail to do
as claying not only clean the surface contaminants but also clean below the surface
its safely remove the contaminants and leave the surface very slick and smooth, u can also use these clay bars for cleaning glass , wind shields windows 
its very easy for clay bars to remove overspray, bugs, tree spa, tar, oxidation, brake dust, industriasl fall outs , acid rains, water marks, as well as also remove overs the years build ups of wax and sealants
if apply corectly than these clay bars totaly safe and non abrassive
differnt kinds of clay bars avilable like strong for very neglected and old paint works, medium grade good to use once or twice a year and very mild ones which even u can use on monthly bases and good for just new cars
clay lubricant is essential part of claying and prevent clay bars to make scratches on surface.
how to apply clay
its very simple, no rocket science
1) shampoo wash ur car and dry surface
2) spray detailing lube on small area let say 2x2 feet area and than softly rub clay on that area back and forth, no pressure , no force, just softly glide over surface, in start may be its resist its mean clay working on surface roughness but than its start gliding freely means its done the work and u need to go next working area / panel
u have to re-shape the bar time to time to have fresh clean surface of clay bar
3) most important thing dont use clay on dry surface as in dry shape its quite abrasive and can scratch the paint so only work on lubricated surface
4) once u done whole car u need to give again a shampoo bath to car with double bucket
never allow ur clay bar to slip from ur hands as in this case it will pick dust from floor and start scratching ur paint surface
remaining clay u can keep store in sealable plastic bag or clay pot if its come with it.
after claying u will have very clean smooth slick surface now u need to protect this surface by polishing, waxing or paint sealant as clay also remove all wax and sealant coats
