If you have been emailed a file in either Microsofts Word or Excel formats, you can open these by saving them to your Google Drive. Click here to Learn how to do that.
Then find the file, you will notice that it has an X icon next to it,
and double click it to View. Once you are viewing it you can select to OPEN in Google Sheets for editing.
Google Drive makes a copy of the file in Google Sheets format. The original Excel format is retained in Drive.