How do I save my scriv project to document folder. And usb drive? It is currently only saved to the desktop
Hi.
Welcome to the forum. 
The project will save in the emplacement where it already is.
So if you wish it to be elsewhere than on your desktop, close Scrivener, and in File Explorer, move it to the place where you wish it to be. (The whole project folder, with the .scriv extension.) Once your project is moved, launch it once by double clicking this time the .scrivx file – with an x -, the file with Scrivener’s logo, inside your project folder, so that Scrivener knows its new location.
As for saving it on a USB key, if that is so you have a backup, rather use File / Backup / Backup Now.
The backups settings are in the options (Ctrl+,) under the “Backup” tab. (Preferably set your backups to be zipped and timestamped.) You may also set automatic backups there.
[I personally wouldn’t trust a USB key for backups. I consider it ill advised.]
If the reason you want it on the USB key is rather so that it is portable between computers, in this case have the project directly on the USB key – (and if so make regular backups of your project on the computer itself, you can’t backup too much – backup, backup, backup) – or alternatively sync between computers using a cloud service.
Last, there is File / Save as, but that is for specific purposes. For any of the reasons above it is not good (or not so good), as it creates a duplicate of your project, opening the door to potential user errors. … Such as working for hours on a project to later realize it was the wrong version of it.