Where are you submitting them to? If you’re hosting your site elsewhere, than you need to build or integrate a forms processor to handle the form submissions.
If your end goal is to get those submissions into Google Sheets, you can use an automation service like Make/Zapier and a bit of programming to connect your form to an automation, and then use that automation to push your data into Google Sheets.
It’s also possible to post directly to Google Sheets, with some setup work;