Most likely you will upload the Excel spreadsheet to create a new Google sheet, however, you can add the Excel spreadsheet to the existing file and include it as a tab. For example, you have a Google sheet about cooking. You can another Excel spreadsheet about cooking to this file as an inserted tab.
Step 1: Open the sheet and in the Sheet, click the "File" tab from the ribbon;
Step 2: Select "Import" from the drop-down list;
Step 2: Click the "Upload" tab and click "Select a File from your device" in the "Import File" window;
Step 3: Navigation to the file location and select the proper file from your computer;
Step 4: Select "Insert new Sheets" in the "Import file" dialog box, and click the "Import Data" button at the bottom;
Step 5: After successfully uploading your spreadsheets, you will see the extra tab newly added.