Additional monitor diplay options

Currently I have a single monitor attached to the HDMI port.  Looking to extend my display to a second monitor via USB-C port. Can I use a USB-C to HDMI / DP cable or do I need a USB dock for 1 additional monitor?  

The instructions on the FAQ suggest using a USB Type C to HDMI / DP Dock.  I want to make sure I can just use the cable on USB-C port to extend to 2nd monitor while still using primary display on the HDMI port. Any clarification would be greatly appreciated. Thanks.