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1. Include the SoftArtisans.OfficeWriter.ExcelWriter namespace in the code behind.

using SoftArtisans.OfficeWriter.ExcelWriter;

2. Instantiate the ExcelApplication object

ExcelApplication oXLAPP = new ExcelApplication();

Unlike the ExcelTemplate object, which represents a single file, the ExcelApplication works as a file generation engine. The ExcelApplication object can be used to create, open, and save multiple workbooks.

3. Create a new workbook with ExcelApplication.Create()

Workbook oWB = oXLAPP.Create(ExcelApplication.FileFormat.Excel2007);

ExcelWriter has the ability to create Excel 2003 (XLS) files and Excel 2007 (XLSX) files, but cannot convert between formats. The file format must be declared when the workbook is created and the file extension of the output file must match when the file is saved.

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4. Access the first worksheet through the Workbook.Worksheets collection

Worksheet oWKST = oWB.Worksheets[0];

You can access worksheets by name (e.g. "Sheet1") or by index (shown above), but ExcelWriter will throw an exception if you attempt to access a worksheet that does not exist.

5. Write the value from the web form into a cell

string value = DataValueBox.Text.Trim();
 oWKST.Cells[0,0].Value = value;

It is important to note that ExcelWriter indices are all 0-indexed, unlike Excel indices, which are 1-indexed. This is importing when working with cells, rows, columns, and worksheet positions in ExcelWriter. You can also reference cells by name; in this case, it would be "A1".

6. Save the workbook

oXLAPP.Save(oWB, Page.Response, "Output.xlsx", false);

ExcelApplication.Save has the same output options as ExcelTemplate: save to disk, save to memory stream, stream back to the client inline, and stream back to the client as an attachment. In this case, we're streaming the workbook back to the client as an attachment.
Remember that the file extension must match the file format specified when the workbook was created.

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SCREEN SHOT

Final Code

using SoftArtisans.OfficeWriter.ExcelWriter;
ExcelApplication oXLAPP = new ExcelApplication();
ExcelApplication oXLAPP = new ExcelApplication();
Worksheet oWKST = oWB.Worksheets[0];
string value = DataValueBox.Text.Trim();
oWKST.Cells[0,0].Value = value;
oXLAPP.Save(oWB, Page.Response, "Output.xlsx", false);