So say you've got iChat (or Adium if you prefer, as I do) open. Your buddy sends you a link to a website which opens in Safari (or Firefox) (or Chrome). On that website you download a PDF which opens in Preview. Just then, you notice that you've been using your Mac for a couple minutes without having any music blaring from your speakers. Open iTunes. All of a sudden, your Desktop is filled with more windows than you know what to do with. Enter Spaces.
Spaces allows users to separate their Desktop experience into organized partitions. These Spaces can be configured to contain only the applications you designate, thus ridding yourself of clutter, without having to close the other programs you need running. Let's take a look at some of the System Preferences for Spaces and see how it can help us organize.
First thing's first. We need to enable Spaces. Go to System Preferences > Exposé & Spaces. Click the Spaces tab and be sure the first checkbox for Enable Spaces is checked (you can also choose to show the Spaces icon in the menu bar).
Now that Spaces is enabled, it's time to get your flow set up. You can add up to 16 Spaces (in combinations of rows and columns limited to four spaces).
Chances are, you won't feel like you need all 16 Spaces. At this point, think about how you use your applications and how you would like them to be grouped. Using the "Applications Assignments"" window, you can click the (+) button to add an application and assign it to a specific Space. If you are a heavy chat user, you may want iChat to show up in every Space. If you are a writer, you may want to keep Pages in its own Space, separate from the distractions that having an open Safari sitting on your Desktop may present (Facebook, anyone?)
Once you have decided how many Spaces you would like, and designated programs to open in specific Spaces (note: if you do not assign an application to open in a specific Space, it will open in the current Space), configure your keyboard and mouse shortcuts.
You can easily switch between Spaces in a variety of ways. Using the quick key designation to activate Spaces (in my case, F8) will bring up the entire grid you have set up. Spaces shows you all the applications you have an active window for, organizing them by the Space they are in (my Spaces grid looks funny because I have a second monitor plugged in).
You can also use your designated keys to switch between Spaces, or use the menu bar icon to select a specific Space. If you forget which Space an open application is in, simply click that application in the Dock, and you will be taken to that Space. You can also use the (Command + Tab) application switcher to take you to an application and the corresponding Space where it resides.
Tip: If you find that you have an application open in a Space and you would rather have it open in a different Space, activate Spaces using your designated hot key (or by opening the Spaces application). Once your Spaces grid appears, simply drag the application window to the Space you would like it be. (Note: for applications with multiple windows open, you will have to drag each window.) For more on Spaces, read this Apple KB article.