The Shrink button on the toolbar () reduces the main window to a smaller size:

As you can see, this hides the Calls/Call Report/Contacts/Actions list and the status bar.  This is useful if you like to leave the main window open while working on your computer, as it doesn't use as much space.

When shrunk, the Shrink button on the toolbar changes into the Restore button ().  Press the Restore button to restore the window to its normal size:

Please note that Shrink and Restore are not the same as the standard Windows functions Minimize and Restore.  Consult your Windows help if you are not familiar with Windows' Minimize and Restore.