The desktop computers that we sell are custom configured Dell Optiplex 3020 systems. Because these computers have built-in, onboard video, in addition to the video card that we install, there is occasionally confusion about what to plug in where. This diagram should help explain how to connect the computer to your monitor and projector(s). Also, note that because the packaging doesn't allow us to leave the WiFi antennas attached during shipping, you will need to attach those after removing the system from the box.
We have shipped these systems with a couple different video cards, so find the diagram below that most closely matches your system for reference.