I'd suggest you to take a look to the help file.
I copied and paste here some text from there:
After you go over it please let me know if you still have more questions.
This help file is a good reference for each of the properties and attributes for the Web Parts. If you would like to learn more on how to use this Web Part, please see the Computer Based Training document.
The qExcelViewer Web Part lets users view their data in Microsoft Excel. The Excel viewer works in conjunction with the qListView.
When the user clicks Export to Excel in the list view, the Excel viewer page will be launched and the data will be opened in Microsoft Excel.
The name of the Session variable where the Excel Viewer expects to find all the information that has been set by a qListView. For this to work, this value must be the same as that of the Session Name property of the qListView.
If set to true, the column name will be displayed in the first row.