To load one of the worksheets in the share library, select the Open ... item from the File menu. When the file selection dialog box pops up, edit the string in the Filter subwindow at the top of the dialog to read /usr/local/mapleV3/share/science/.ms and then click on the Filter button at the bottom of the window. Setting the filter string tells Maple where to look for files to load. A list of file names ending in .ms should appear in the Files subwindow of the dialog. Select one of the files, for example area.ms, and click on the Load button.
After you've looked at one of the sample worksheets, you can look at another by repeating the process above, but selecting a different name. The filter string, however, will stay the same until you change it, so you won't need to edit it every time.