Hokay.
When you click the box for the add-in and click ok in Excel, nothing "big" happens. All it will do is add a new menu between Window and Help on the menu bar.
Just select the area you want in the sheet, and go to the new HTML Maker menu, and select the option to convert the sheet. When it brings up a new browser page, click the button for 'copy code' and then just paste that into the message box here at the board. Note: Don't click 'preview' if posting HTML Maker code!
Don't panic too much if it doesn't work correctly sometimes when you post a message. Sometimes, it just gives more code than the message box can take, and will go a bit wonky. Just edit your message to take out the code, and try a smaller selection from your sheet.
Hope it helps,