Photoshop is basically made up of four areas: the menu bar, at the top, the toolbar just below it, the toolbox on the left and the palettes on the right. The menu bar and toolbox always stay the same, as they contain the different modes and options that you can choose, but the toolbar changes depending on context.
The palettes are there to show the current status of your image, including the history of all the actions you have used and a thumbnail overview of how the 'big picture' currently looks.
To demonstrate the way the interface changes as you use it, try selecting the type tool from the toolbox (the one that looks like a capital T). You will see straight away that the toolbar changes entirely to allow you to set font name, font size and so on.
Now notice the updates in your palettes. The type tool modification will be added to your history in the history palette, and a new layer will be generated for your text and displayed in the layers palette.
The toolbox or the menus will most likely be the starting point for projects done with in Photoshop. Everyday tools such as selecting, filling and making shapes will be found in the toolbox. More advanced functions, such as blurring sharpening and most other effects Photoshop can produce are found in the menus, most of which are found under the Filter menu.
You can adjust the settings of tools from the toolbox using the toolbar. When doing this, options from the menu will typically open a dialog box. Should you want to change any actions you have made to your image, simply do so through your palettes. While the palette history is helpful, palettes have other uses also such as changing colors.