To save the results of your work to an image file, use the File > Export.. menu item or the key combination Shift + Cmd + E.
When you export a file, you can save in a variety of file formats including JPG, TIFF, PNG and even PSD. Each file format has its own unique set of parameters which are standard macOS system options.
To save your work in progress, press Cmd + S on your keyboard or choose the File > Save... menu item. Your work is saved in its current state so that you can later continue from the same point. The file is saved in the proprietary Aurora HDR 2018 file format and cannot be opened with another application. For other software to use images created using Aurora HDR 2018, you’ll need to Export the file (see above).