i hear alot about this for on cars ect but what exactly does it do? and how much do they cost?

Clay removes any contaminants on the clearcoat of your car, ie. tree sap, road grime and any tar thats left after inital de-taring, leaving your car ready for polish and waxing.

In my opinion its a must for getting a clean smooth base for polishing/waxing, the difference between a clayed and an unclayed car is night and day to the touch.

Get on to ebay and get some of the Bilt Hamber clay, in around a tenner as far as i remember, and doesnt need lube(just plenty of water)unlike some other clays that fleece you having to buy the lube as well.

Wash your car as usual(preferably with a wash mitt) then break about an inch and half square piece(or there abouts)off the bar,

wee tip here put the piece you broke off into a glass of warm water as this will make it easier to mould the clay into a flat circular shape to use on the car,

keep the glass of warm water with you as you will have to mould the clay
again at some stage, so just plonk it in for 20 secs or so to make it malleable

get your spray/mist bottle, fill with water(i like to put a wee bit of my car shampoo/wash in as well, just for luck lol)and wet the area down, do a panel at a time and keep the water going over the clay and surrounding area as you work.

Just take it easy and make sure your clay is moving freely over the bodywork, if its sticking your not using enough water to lube the clay, and keep kneading and turning the clay as it gets dirty(will be easily seen).

Its not hard to do, and gets great results, just remember(again lol) to get the Bilt Hamber stuff as it saves you needing the lube.