Here are the different ways that you can save new files and changes into SuiteFiles.
Saving a brand new file
You can either create a new file in SuiteFiles or save a file from your desktop.
If you want to save a new file you created on your desktop, you can either save it to the SuiteFiles Drive folder in Windows Explorer or save it to your desktop and drag/drop it into SuiteFiles Web (read: How to upload files).
Saving changes made to a file
If you choose to edit a file in the web browser, changes will save automatically. There is a 'Save and close' button if you wish to use it, but otherwise, all changes will save automatically.
If you edit a file by clicking 'Open in Office', the file will open in the relevant Office desktop program. From there, click 'Save' to save your changes back to SuiteFiles.