I HAVE A PROBLEM THAT SINCE DOWNLOADING WINDOWS 10 - I CANNOT OPEN MY EXCEL FILES TO WORK ON ??

IT LOOKS LIKE TEY ARE ABOUT TO OPEN BUT DON`T - AFTER A FRUSTRATING NIGHT TRYING TO GET ON WITH MY BUSINESS THRU THIS - I SOMEHOW OPENED ONE - BUT ONLINE EXCEL ?? WHAT IS THIS AND WHAT IS THE DIFFERENCE WHEN I HAVE TO SAVE DOCUMENTS AS I AM CONFUSED ...I WANT IT SI PLER JUST TO OPEN MY EXCEL DOCS I SAVED

THANKS