Don't want to take you hands off the Mouse to activate Dashboard? Want to click a button on the mouse to start Expose? OS X Has just the thing for you. It's called Active Screen Corners (a.k.a. Hot Corners). Open System Preferences, and then choose Dashboard & Expose.
Notice above, each corner has a corresponding Dialog box. Click on each box to choose the option for the corresponding corner.
Here I am choosing 'Dashboard' for my bottom left corner. I simply move my mouse to the bottom left corner to activate it.
If you hold down a Modifier key, such as COMMAND, CONTROL, OPTION, or SHIFT when you click on the dialog box, it gives you more flexibility. If I were to choose this option option, I would hold down COMMAND and move the Mouse to the bottom left corner. Download the Podcast.