In the same way you do on iTunes: Previous Track, Play/Pause, Next Track, Volume, and Shuffle On/Off.
The exception is the information control, the egg with the arrow. Click it to extend an information window. Click the egg to close the information window. The information window has the following elements:
Click the information window to change the time. Click an active source icon to select the source.
* The Widget is initially set to scroll this information if it's too long for the window, although you can turn this feature off if you think this might be degrading your computer's performance. Right-click the Widget, choose Widget Preferences, and clear Scroll Lengthy Titles.