Why are my objects in all layers? I have the same objects in all 20 layers.
If I delete one of them, the objects in all twenty layers are deleted, not the single one.

I would like the have my object in the first layer only.
Any solutions?
Try selecting the object and pressing M to move between layers. If all the layers are selected in the dialog which subsequently appears, press 1 (or click on the first layer in the dialog with  LMB) to move the object to just that layer.