You'll see here a different icon amongst the image and folder icons you've seen before... and an odd filetype, .ssh.
Now you'll also see Save and Open buttons on this screen, before you render the sheet.
And this is the save screen. .ssh is a Sprite Sheet File, and stores all the information involved in the project.
So here I have another sheet open (featuring a sprite made by yours truly).
And if we open the .ssh file we saved just a minute ago...
Everything pops back up, including new lines and the background colour! Your computer should also link .ssh files to this app, so you can load a project simply by opening a file directly.
Note that .ssh files are fairly large, as they are essentially storing all of the images involved in the project in one file. I may add another filetype later that has a smaller filesize, but stores only the location of each file, so it won't necessarily open the same project if you change the source.