Photoshop has many, many windows. Luckily you don't need to learn them all at once: focus on the Info, Navigator, and Layers windows. After that, learn the Options,History, and Actions windows.

You can arrange your document windows to overlap or side side by side. You can also specify that the hand and move tools affect all windows, or just the top one.

Photoshop can organize your workspace in ways that make sense for various taks (retouching photos, web design, etc.).

I strongly suggest that you learn to work with the windows in these standard locations. Moving windows around quickly creates a disorganized workspace, and even if you find an arrangement that you like it will not be pre-set if you have to use a different computer. Stick to the standards.

Use the Actions window to record and play back a sequence of operations. For example, you can use this window and the File > Automate > Batch... command to resize and add a copyright notice to every image in a folder.

Use the Animation window to create animated GIF images.

Use the Brushes window to choose from a selection of pre-built brushes, and to store the brushes that you create.

Use the Channels window to work with the color channels (i.e., red, green, and blue) of your image individually. You will often do this when color-correcting photographs and converting color images to black and white.

Use the Character window to choose the font, size, spacing, etc. of text.

Use the Color window to see and change the component values of the current color. Personally, I never use this window — I use the Color Picker instead by clicking on the foreground or background color in the Tools Window.

Use the Histogram window to see the distribution of grayscales and colors in an image. If you create a selection (i.e., use the marquee tool) the histogram only includes selected pixels.

Use the History window to go 'back in time' and undo past actions. This is particularly useful when used in conjunction with the history brush tool.

Use the Info window to get information about the current selection and the pixel under the mouse. Note that you can view pixel values in any color space (RGB, HSV, CMYK, LAB, or Grayscale) and not just the color space of the document.

The bottom of the window displays options for the currently-active tool.

Use the Layer Comps window to keep track of different variations of your document. This lets you quickly show your clients the three or four ideas that you have for their website, for example.

A photoshop document is composed of several layers, like sheets of transparent glass. Use this window to show, hide, rearrange, and blend the layers in different ways.

This is probably the most important window in Photoshop, so it's a good idea to learn to use it well.

Use the Navigator window to quickly move around your document when you are zoomed in.

Use the Options window to specify options that affect the current tool. For example, you would use the Options window to specify the tolerance of the magic want, the feathering of a marquee, or the opacity of a paintbrush.

Use the Paragraph window to set the inter-paragraph spacing and margins of text.

Use the Paths window to organize the vector-based paths in your document. Unlike layers, paths are not distorted when you resize the document.

Use the Styles window to choose from a number of preset styles to apply to a layer. A style is a combination of filters and layer effects that might, for example, define the 'look' of a button on a website. You can also create your own styles.

Use the Swatches window to keep track of your favorite colors, pattterns, and gradients.

Use the Tool Presets window to record and retrieve the current tool settings. This allows you to, for example, define a standard font, size, and color to use with the text tool.

Use the Tools window to choose which tool to work with. This window is so ubiquitus that I don't even think of it as a window — it's simply a core part of the Photoshop UI.

The bottom of the Window menu lists all of your open documents.