As soon as i delete the edge loops i get this surfaces..how do i make it go away?
That is called z-fighting. It means that you have 2 face really close and Blender is having trouble determining which one to display. The back and fourth is what you are seeing. So you just need to either move the faces further apart or delete one of the faces.
thank you..in the tutorial i was watching the z-fighting didnt happen tho
You must have duplicated the faces somehow, before you separated it. If you hide the bumper object there should be holes where the bumper pieces where separated from the crate object. Looking closely It kind of looks like there may be 2 crates. Select the create object. Then tab into edit mode put mouse cursor over a vertex and press L to select linked. Then press H to hide and make sure that there isn't 2 crates on top of each other within the same object.