Let's say we have a red logo and a picture of the car 

The white thing on a Black Background

Click Overprint

Print the Black and Print the Next Colour on Top of it. 

So with white objects that are set to Overprint, they will disappear on print because white is not ink. 

In reality, the white gets knocked out from the colour beneath. But when the white is set to overprint, the white will not knockout but rather be removed because it's intended to print as a second pass after the first set of process c