When your Signup Flow widget is submitted (or skipped) you can choose to either redirect to a thank-you page of your choice or close the widget so the new subscriber will stay on the same page.
To set your preferred behaviour, go to your Signup Flow editor, click on the "Settings" tab and scroll to the "After submission" section.
If you choose to redirect to another page, you will need to enter the URL of the page you want to redirect your subscribers to.
If you choose to close the widget instead, you can click on that option.
If you want to show a thank you message, you can set it to that as well.