Stamped?
Unless changed, the first layer is called the Background Layer. The Background layer can not be edited.
If you want to make it an editable layer, click on the lock icon to the right of the layer name. Unless you change the layer name, it will then be labeled Layer 0.
To make a layer adjustment, or to make an Adjustment layer? Two very different things.
If you press your keyboard's F! key with Photoshop open it takes you directly to the Adobe Community Help​ web page.
If you want to duplicate the selected layer, use the keyboard short-cut --- Ctrl-J.
To make an Adjustment layer use the Adjustment layer icon (the dark/white circle) along the bottom of the Layers work pallet.