The explanation of how to use the Object Browser built into VB.NET in the book is very good. (If you want more, however, try the MSDN Super-Easy Guide to the Microsoft Office Excel 2003 Object Model.) But sometimes, a picture is worth a thousand listboxes.
To see what the Excel 2003 object model looks like in one diagram, check out this page from Microsoft MSDN. A few minutes browsing this will give you new respect for the huge volume of code you're making available to your program when you write the simple statement:
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CreateObject("Excel.Application")
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If you have the Excel 2000 version, that model diagram can be found here. An explanation of the model ... from the MSDN VSTO pages since Microsoft understands that VSTO will place new demands on developer understanding of the model ... can be found here.
But as massive as the Excel object model is, the Word model is even bigger! To browse through the Word object model, go to this Microsoft MSDN page. Word 2000 can be found here. And the description of the model is here.