Photoshop provides guides to help you align content vertically and horizontally within your image and a grid to help you position things by eye as you drag them with your mouse. Guides appear as lines that float over an image and do not get printed.
We can move, remove or lock a guide to avoid accidentally moving it.

Layer masks let us hide or reveal portions of the artwork on an individual layer. When hidden, that part of the layer becomes transparent.

We can control the amount of artwork that can be hidden or revealed on a layer. This is done using the two steps:

	Firstly, make selections for the mask
	Then the mask is painted using black, white or shades of gray.

	Making selections
	Applying black, white or shades of gray
	White - reveals artwork
	Black - hides artwork
	Gray - hides artwork partially

By default, a layer is linked to its layer mask, as indicated by the link icon between the thumbnails in the Layers palette. The layer and layer mask move together in the image when we move either one with the move tool. We can unlink the layer from its layer mask by clicking the link icon. Unlinking the two lets you move them independently and shift the mask boundaries separately from the layer. To re-establish the link, click between the layer and layer mask thumbnails.

In a clipping group, the bottom-Most layer or base layer, acts as a mask for the entire group. For example, we might have a shape on one layer, a texture on the overlying layer and some text on the topmost layer. If we define all three layers as a clipping group, the texture and the text appear only through the shape on the base layer and take on the opacity of the base layer.

Note that only successive layers can be included in a clipping group. When we create a clipping group, dotted lines appear between the grouped layers in the Layers palette.

The name of the base layer in the group is underlined and the thumbnails for the overlying layers are indented.

The clipping group is assign the opacity and mode attributes of the bottom-most layer in the group.

An adjustment layer can be applied to an image to apply color and tonal adjustments without permanently changing the pixel values in the image. Because the change occurs only on the adjustment layer, this feature enables experimenting with different colors with ease. Changes can be safely undone, if we decide to return to the actual pixel values, by hiding or deleting the adjusment layer. When an adjustment layer is active, the foreground and background colors default to grayscale values.

When an adjustment layer is created its effect appears on all layers below it. This lets us to correct multiple layers by making a single adjustment rather than making the adjustment to each layer separately.

Each layer mask in a file increases the file's size. To minimize the size of our files, it is important to remove or merge layer masks after the final design is completed. The Remove Layer Mask command is used to remove the mask on the layer with the artwork on the layer.

When we flatten a file, all layers are merged into a single layer. Flattening sends a file out of proofs. But we have to be sure to save a copy of our file that includes all layers if we want to edit the original image after the conversion. In a flattened image, all visible layers are merged into the background, greatly reducing file size.