Can filling out a form be interrupted, be saved and continued later?

Yes, there are 2 ways on saving the form and continuing it later. Please check these 2 guides:

How to Enable Auto Fill Feature - http://www.jotform.com/help/227-How-to-Enable-Auto-Fill-Feature
How to Save Forms to Continue Later - http://www.jotform.com/features/save-and-continue/

Please take note that the Auto-fill feature will save the data in the local browser, so it is only possible for the form to be continued on the same computer and same browser.