While Google Drive CAN open Microsoft Office files (Word, Excel, Powerpoint), editing tools are limited and some things might not show up correctly.
In some cases it's better to convert them to Google's formats (Docs, Sheets, Slides)
It's a very easy process.
With the Microsoft file open, click File -> Save As Google...
You'll briefly see this message:
Your new Google Format file will open up, and you'll see a message confirming.
You can either delete the original file, or hold onto it for safekeeping.