Select and configure icons, press the download button. Fontello creates all the necessary files in single zip archive. We strongly recommend you store the content archive on a version control system. For example, here, on github :) . That will not cost you anything, but allow to keep data safe, track changes and roll back mistakes. Also, you will not depend on accounts on 3rd-party sites, on browser changes and on hard drive crash. See, how we store icons on fontello itself.Sometimes you need to modify an existing project - add new glyphs and so on. Every zip-file, generated by fontello, contains config.json in root. That's configuration of your project. You can always import it back to continue your work. Let's look at all possibilities.
Just drag config.json or the whole project's zip archive to fontello page.