Included in the box with the UD-3900C is a short quick start guide that shows you how to get started using the dock. A PDF version of the quick start guide is available here
To expand on the information within the quick start guide, the first step is download and install the dock's required DisplayLink driver on the host system (please see the 'Downloads' tab for a link).
Once the required DisplayLink driver mentioned above has been installed the next step is to physically connect everything together.
In the box with the dock there should be a power adapter, power adapter prong (the blades that go into the power outlet) and one USB-B 3.0 to USB-A (with USB-C adapter) cable.
Slide the prong into the power adapter until it 'clicks' into place (this may have been already for you, depending upon the region you purchased the dock within). Then connect the power adapter to the barrel-shaped power inlet on the back of the dock and also to a working electrical outlet. A solid blue light should appear on the front when the unit is getting power and ready to be connected to your system.
Now connect one end of the USB-B 3.0 cable to the laptop host port on the back of the dock (the one with a small laptop icon next to it) and the other end to either a USB-A or USB-C port on your laptop. Once the dock is connected to your system, you can attach one or two additional monitors to the HDMI video outputs on the back of the dock using standard HDMI to HDMI video cables (cables with a HDMI connector on both ends).
** When connecting the monitors, one thing to double-check is that the source video input setting within the monitor is set to the correct HDMI input. This is especially important when connecting displays that have more than one HDMI input, because displays with more than one input may not always switch to the preferred one automatically. **
Once the monitors are connected, Windows should automatically 'Extend' your desktop to the additional monitors. If this is your first time using a system with more than one monitor, we have made a series of short tutorial videos that demonstrate how multiple displays work that many find helpful:
Once the monitors are working, you can then connect any other USB devices (like a keyboard or mouse) to one of the four USB 2.0 ports on the back of the dock as well as an Ethernet cable (if you need one) or headphones or speakers.