Important tools include: Crop tool (remove all but a specific area of your image), Brush tool, Clone tool, Heal tool (advanced Clone tool), Gradient fill tool, Paint Bucket tool, Eraser tool, Dodge/burn tool (makes things lighter or darker), Sharpen/Blur tools, etc.

Palettes are the little windows on the right side of your screen that contain all kinds of important information. You can hide them all temporarily by pressing Shift+Tab. Use the same key combination to get them back.

Some important palettes to have open are: Layers palette, History palette, Navigator palette (for zooming around your document), and the Character palette for working with text (you can find this one by going to the Window menu). If you ever "lose" a palette and can't find it, look on the Window menu.

Hold down the spacebar and your left mouse button, then move your mouse around if you want to pan around your image. To zoom quickly, you can hold down the Alt key (next to the spacebar) and roll the wheel on the top of your mouse.

You can also use the Zoom tool on your toolbar (it looks like a magnifying glass). Hold down the Alt key when using the Zoom tool if you want to zoom out.

It's easy to make mistakes in Photoshop, isn't it? To undo a mistake, use the "Step Backward" command on the Edit menu. This is better than "Undo" because it lets you undo many times, rather than just once.

The "Step Backward" command is stepping backward through your "document history," which is a list of things you've done since you opened your document. You can find this history list in your History palette. To undo using the History palette, you can click on the name of the last step you performed before you made a mistake, and the document will revert to that step.

It's simple - we need to tell Photoshop what specific area of our document we want to affect, so the tool we use doesn't change the entire document.

Rectangular Marquee tool, Elliptical Marquee tool, the Lasso tools (Lasso, Polygonal Lasso, and Magnetic Lasso), the Magic Wand tool (select by color - don't forget to change the Tolerance at the top of the screen), and the Extract command on the Filter menu.

You can use the Shift key in combination with any selection tool to add to an existing selection. Likewise, holding down the Alt key will make that tool subtract from an existing selection.

Layers allow us to combine many images and different text areas in one document without destroying our original image. This way, photos and text are stacked on top of each other, rather than irreversably replacing what's beneath them. This way, we have the freedom to move items around as much as we want before calling our changes "final."

Layers also have two other important features - Blending Modes and Opacity. Using Blending modes (the menu that says "Normal" at the top of the Layers palette), you can combine a layer with the layer beneath it in new and fascinating ways. Using Opacity, you control the transparency of a layer, meaning "how much you can see through it to the background."

If you want a command to affect a specific layer, be sure to click on the layer name in the Layers palette to select that layer first. To rearrange layers, just drag and drop them in the order you want. This doesn't work with the background layer, so you can right-click it and click "duplicate layer," then move the duplicate around.

To hide a layer, click on the "eyeball" icon next to it. To rename a layer, double-click on its name. To edit a text layer, double-click on the "T" icon next to its name.

When we start an image from scratch, we need to tell Photoshop the size we want to work with.

Most computer screens work at about 72-150 dots per inch (or dpi - a dot is the same as a pixel, as far as computer screens are concerned). This is actually quite low! Most printers print at least 300 dots per inch, and books are often printed at 1200 dots per inch. This explains why, even though an image may look good on your computer screen, it can look terrible when printed out or enlarged.

When you scan photos with a scanner, you are able to choose the resolution you want the image to be scanned at. If you plan on printing the scanned image, be sure to scan at at least 300 dpi (I recommend 600 dpi if your computer has enough memory). To display your image on the web, make a copy of it and resize it using the Image size command on the Image menu. If you're emailing a photo, 640x480 pixels is a good size to reduce to. This way your friends won't get mad at you for sending them huge images!

Most digital cameras shoot at at least 4 megapixels now. This is 2272 pixels wide and 1704 pixels tall (though it varies slightly by camera brand). This is very big - you wouldn't want to email your friends images of this size for on-screen viewing, but you would want to keep your originals at this size so they look good when you print them out. Again, it's the difference between your low-resolution screen and your high-resolution printer.

GIF, JPG, and PNG are the most popular web-and-email-ready photo formats. A Photoshop PSD image can only be opened by Photoshop (and a few other expensive programs), so unless your friends have Photoshop, you'll need to use the Save for Web command on the File menu to save your photos in GIF, JPG, or PNG.

JPG is a great compromise between image size and image quality. However, JPG images will degrade a bit every time you save them. Not good! This is why you should keep your originals in either PSD, or just save to PNG, another good image format that your friends will be able to open. PNG files don't degrade over time, but they are a bit bigger than JPG files.