Here is how to get the most use out of this great OS X feature. First we will set the Expose Preferences.
Select Preferences from the Apple menu at the top left hand corner of the screen.
Select the Expose & Spaces icon from the System Preferences window.
Select the Expose tab from the Expose & Spaces Preferences window.
There are three ways you can use Expose. You can have Expose show you all open windows, all application windows, or the desktop.
To set the keyboard shortcuts for Expose use the three dropdowns entitled "All Windows", "Application Windows" and "Show Desktop". The default settings are F9 for All Windows, F10 for Application Windows, and F11 for Desktop.
NOTE***: Apple's new keyboards change these defaults if the proper drivers are installed.
Set the active screen corners by selecting an option from the four dropdown menus at the top of the Expose Preference Window. Each dropdown represents a corner of the screen. If you move the mouse to that corner it will activate whatever action you selected from the dropdown. Notice that you can even set none Expose actions here like starting your screen saver!
For example: I set the bottom right hand corner dropdown to All Windows. This means whenever I move my mouse to the bottom right hand corner of the screen it tells Expose to display all open windows.
Press Command+q to quit System Preferences.
Lets try to use the Expose shortcuts we just made. Open a few programs so you can see how this works.
Hit the F9 key on your keyboard. Exposé instantly tiles all of your open windows, scales them down and neatly arranges them, so you can see whats in every single one.
Move your mouse from one tiled window to the next and youll see its title displayed right in the center of the window. When you find the window you need, just click on it. Magically, every window will return to full size and the window you clicked whether its a folder, a PDF, a QuickTime movie or a Word document becomes the active window.
Hit the F10 key on your keyboard. Notice that only the active application's windows are now tiled. So for example if you are working with multiple Firefox windows this option would tile the Firefox windows and hide all others. Click the window you would like to work with.
Hit the F11 key on your keyboard. Now all windows are hidden and you can see the desktop. Press F11 to make your windows reappear.
Now lets try to use the mouse Expose shortcuts. Remember we set the action for each corner of the screen. My preference is set so that when I move the mouse to bottom right and corner it makes Expose tile "All Windows". Try moving the mouse into the corners you preset. To make return things to normal just move the mouse to the same corner a second time!