If you’re looking to take advantage of content from within WordPress that doesn’t use its templating system, one means of doing so would be the Ajax API. Your client-side code would call WordPress Ajax functions that would return the content you desire.
As to the spreadsheet matter, this is not standard WordPress behavior, but you can find various plugins that will allow you to import .CSV files (which can be exported from within Excel) as content. I am doubtful that you will find plugins that can read the native Excel format, but could be mistaken.