Layers are like stacked images on panes of glass. You can “slide” a layer in a stack to change what portion of its content is visible in relation to the layers above and below.
Drag within the image to slide the selected layer or layers to the desired position.
Press the arrow keys on your keyboard to move the layer or layers in 1‑pixel increments, or press Shift and an arrow key to move the layer in 10‑pixel increments.
Hold down Shift as you drag to move the layer or layers directly up or down, directly to either side, or on a 45° diagonal.