Overspray/ Clay bar info questions

[Kiss My SS]

Ok, so I backed the Monte out of the garage at my parents place and it was dusty as hell. I washed it and it still looked dusty. I looked close and realized the the "dust" was really a fine mist of overspray. I have no idea what I would have driven through that would have caused this. Nobody there has painted anything in months, and when they did the car was not out. I have heard that you can use a clay bar to remove the overspray. I have never used one and would like some more info on how to use them and what brand to use. Or is there a better way to remove this overspray? Thanks for any help you can provide.