If you created a new document in the generator, after clicking on the save icon you will only see this option.
This function will create a new file that will be stored and listed on your profile.
In order to save you must select at least one tag for the document.
If you opened an existing document that you created previously, the save panel will show you two options: you will be able to save it as a new document and keep the old one, or overwrite the previous document.
If you opened an existing document that somebody else created previously, the save panel will show you only the option to save it as a new document on your profile.
Any changes that you made will be saved on your copy of the document just like if you created a new document from scratch, the document created by the author will be unaffected by your changes.
If you have private slots left, you have the option to make your diagram private while you are saving.
To do so you need to select the 'Private diagram' checkbox, this will use one of your private slots.
You can delete your documents and organize them in collections from your profile.