If you open the output excel file within the browser(inline) , you can just output a html with Response.Conten tType = "applicatio n/vnd.ms-excel". In the html you can use a table to render you data.
If you need to generate a complex excel file and you don't know what the html codes should be, you can:
1. create a similar excel as what you want via Microsoft Excel.
2. save it as a html file, you will get the html codes.

I suggest to use a*c# excel component Spire.XLS, I use it long time, quit good.
It*supports importing/exporting to XLS, XLSX, CSV and HTML files.
May help to you.

Easiest way to export to excel using a c# excel component Spire.XLS, I use it long time, name Spire.XLS, may help to you.