It very much depends on whether you want people to be able to interact with the workbooks and the data held in them.
The quick and easy solution to just display the content of a spreadsheet without giving interaction with it is File, Save as Web Page...
All this does is create a simple HTML file that displays the data held on the sheet or entire workbook.
You can also embed Excel spreadsheets into HTML documents as a data object, but much depends on the software you have available and your web hosting package as to whether or not this will work as you might like it to.
If you want user interaction we start getting a bit more complex, so if you want this, post again and one of us will walk you through some options.
It would help to know the version of Excel you are running and whether or not you have any web authoring software.