Download and install Steinberg Download Assistant (click). Run Steinberg Download Assistant and download the full installer for your version of Cubase. Run that full installer and install everything. Run eLicenser Control Center, which will have been installed for you, and activate using your Activation Code.
You don’t need a USB eLicenser for Cubase Elements - but if you activate to a USB eLicenser you cannot move the licence to a soft eLicenser (which is stored on your computer’s hard disk / SSD).