Depending on what you would want to achieve, you can create a new spreadsheet in your Google sheets or import and already existing blank or old spreadsheet to Google sheets. To create a new spreadsheet, you will click on the new spreadsheet option from the Sheets Homepage. Assuming that you already have a G suite account, from your Google drive, you will click New - Google Sheets - Blank spreadsheet.
To import, go to Drive, click New and then file upload. Choose your already existing spreadsheet from your PC and add it to the drive. While in drive, right click the spreadsheet you would like to convert and the select open with Google sheets