You will need to use the COM Interop to work with Excel, 1st you need to have Excel or Office installed. Now the bad, with the different versions of Office it can be quite daunting to keep it all in order. There are versions of Office that implement some methods differently or do not support features that other versions do. Your code will need to have checks in plcace to prevent trying to do something that a certain version does not support or crashes will happen.
With warning in place, here is a tutorial that will get you started.
How to: Use COM Interop to Create an Excel Spreadsheet (C# Programming Guide)