Multiple Layers
Photoshop helps you save time by allowing you to work with multiple layers at once.
This is useful when you create more complex images and need to reposition, align and transform more than one layer at a time. The ability to link layers lets you do this with ease.
To link layers click one of the layers to start the link (active layer). To link any other layer to the active layer simply click the little box directly to the left of the thumbnail and a chain icon will appear there, indicating that the layers are linked.
You can link as many layers as you wish, to unlink a layer just click its chain icon.
To align and evenly distribute Objects
The Align and distribute option appears in the options bar if at least three layers are linked.
To center Objects on a page Click the background and link it with the objects you want to move. Choose the Align Vertical center button and click on it.
