No mate, it's easy, just make sure your cars JUST washed and dry, if you buy a kit like the Meguires, it will contain the clay bar and a lubricant, spary the lube over a managable area first, say a third of your bonnet, then warm the clay in your hands, so it softens up, then gently press onto the paint serface and slowly rub up and down the lubricated area, pretty soon the clay will flatten to the bonnet serface and stat to pick up crud, have the spray bottle of lube in your other hand, so if you feel the bar dragging, you can spray some more.
This will leave a milky film all over the paint work, so you will need to wash the car again, then leather off and rewax straight away
