Howto Mount Android USB on desktop or laptop.
Its not immediately obvious how to do this.
You've connected your Android by USB, get the 'USB connected' message, and then the USB icon top left on the screen.
But no volume on your desktop.
What you need to do is to press and drag in the notification area, and select 'USB Connected'. It then asks if you want to 'Mount' or 'Don't mount'. Select 'Mount' to have the SD card mount on the desktop.