Any spreadsheet app should have some sort of import/export support ON LAUNCH DAY. The omission looks sloppy.
Just to make it clear, it's not that hard to do it. Here's a very basic example in javascript that took roughly 3 hours of time (this parses enough of the XLSX format to generate a CSV output with a few integers and strings; requires html5 file API to be able to manipulate the file in your browser. Best results on chrome):
Sorry, but without a way to bring data in or out this app looks unfinished.