Section painting

Hello,
I ve done a few paint jobs in the past, and am artistically inclined, but I was just woundering how sections can be done, im looking to air brush some stencils onto a car, but its only a design on the hood and side panals. Im thiking just spraying over the clear coat then re sealing it would be a mistake, though im not farmiliar with anything other than stripping the whole car.