To save your package to a cloud storage service (such as Dropbox, Google Drive, OneDrive, etc), click on the Save to Cloud button.
The button will change into a small animated circle as it gathers the settings into a file for publishing. When it's done, a popup will open, allowing you to connect a cloud storage service if supported by the Assembler (or just navigate to your files if you've already linked an account).
Once you've opened the location or folder where you want to save the package, you don't need to click on any of the files within it. Just click the blue Select button in the bottom right corner to save your file to the cloud.
For more detailed information on how to manage the cloud storage popup, see Cloud storage management.
After you save the package, you can still go back to previous sections of the Assembler to make more changes and save again - the files are not "wiped" from your browser until you press the Reset link.