A new spreadsheet is created, and opens in a new browser tab. Every response appears in that question's column, along with some extra data like the time that the response was submitted.
Now you can even use the tools available in Google Sheets to do some extra analysis of the responses, or even download the spreadsheet to use in Microsoft Excel.
Future responses will be added to the spreadsheet as they come in. To stop, you need to unlink the form from the sheet.
From the Responses tab, click the More button.
Select Unlink form.
A confirmation dialog box comes up, informing you that future responses won't be added to the spreadsheet anymore but existing responses won't be removed.
Click the Unlink button.
The form is unlinked from the spreadsheet, and the Sheets icon on this page will no longer link to it.