Yes, users can save an incomplete form submission and continue filling out the form at a later time. To enable this feature, go to Settings → Advanced and check the option Allow respondents to save the submission and resume later.
A new button will show up at the bottom of your form: Save for later. When clicking it, users will be given a link and instructions for using it.
When accessing the link, users will see the form with the content they have already filled out. They simply need to continue filling out the form and click Update Submission when they are finished.
The link for resuming the entry is also sent by email to form respondents. Just select the email field from your form in the Reply-to-email dropdown in Notifications.