Understanding states and snapshots in Photoshop

You can’t go too far in your use of the History palette without understanding two important concepts, as well as how the concepts are different:
-->States: States are just another way of saying steps. At any given point in your imageediting activities, Photoshop saves your individual edits into states. By default, Photoshop remembers 20 states for an image.

-->Snapshots: You can save temporary copies of an image, each containing all its various states. For example, say you make six edits to an image before you take a snapshot. The snapshot shows the image, but it also contains a complete history of the six states. Make a few more changes, and take another snapshot: The new snapshot contains the six states you made previously, as well as any new ones.

When you have these concepts down, you can get to the business of understanding how the individual tools in the History palette use states and snapshots to help you go back in time (and back to the future again) to undo, redo, and modify each miniscule edit you make to your images.