History state is a state of an image: you added type to your image, to go back to state without type or before you added type click on history state before action of adding type in History palette.
In Photoshop the Command (Apple) key + Z will Undo your last action using the Option (Alt) key with Command + Z will repeatedly Undo your previous actions - effectively scrolling back up through the History palette.
by undoing last action Ctrl+Alt+Z or from history palette , from Window menu choose history to open palette , then find action by name ( for example : fill layer ),but be careful because if you have other actions below chosen (performed after action you want to recover ), will be deleted permanently
Prior to CS4, panels were referred to as palettes. A panel or palette is a box (usually located on the right hand side of the screen, but moveable) that allows you to change options associated with a Photoshop feature. For example, the layers panel or palette is used to manipulate layers; the character panel or palette is used to manipulate text.
In image window you have image to work with, and in palette you have tools and commands to enhance image displayed in image window
Alpha channel, take a look at CHANNELS palette
Use Transparency slider in LAYERS palette.
If the Layers palette is missing, you can return it by clicking on the "Window" menu near the top of Photoshop, then selecting "Layers" to ad a checkmark next to it, indicating that it is now visible. Photoshop also allows palettes to be un-docked from the program and dragged around anywhere on your screen, not just in the Photoshop window, so if you have a dual-monitor setup, make sure that you didn't somehow hide the palette on your second monitor.
From PATHS palette at right side of screen (Window > Paths). Take a look at bottom of palette, there are options to fill, stroke path or to load it as selection if you need.
Using blend modes. Blend modes U can access from top of LAYERS palette for example
Select that layer (click on it on LAYERS palette) where is something You want to add glow effect then click on fx at bottom of LAYERS palette and choose Outer glow effect (or Inner).
Select layer You want to transform (click on it at LAYERS palette) then press Ctrl + T.