The Excel results spreadsheet tells you how many respondents you had who left any answers, and how many of them submitted their responses. However, you can also find these numbers and the number of overall visitors to your survey in an easier way by going to Team settings. Under the Reports tab you should be able to find a button that says Download questionnaires report as CSV. Please note that if you have several draft and published questionnaires, it may take a moment for the report to be generated!
The report is in CSV format, which means that to make it legible you need to arrange the text to columns in Excel. To do this, go to Data > Text to Columns > choose Delimited and click Next > choose Comma and Tab and click Finish. The resulting file should look similar to the image below (click it to make it larger).
One row represents one questionnaire. The All Respondents column includes the number of all visitors to the survey, including those who never left any responses. Submitted Respondents is the number of respondents who clicked 'Done' at the end of the survey. The number of Visible Respondents with Any Meaningful Data tells you the number of respondents who left at least one answer.